Protecting Your Brain From Blast Injury

Welcome to The Debrief. In today's episode, we're going to talk about an issue the New York Times called one of the most significant hidden health crises in the modern military: mild traumatic brain injury caused by blast exposure. More specifically, what repeated exposure to the overpressure from explosive breaching, flashbangs, and large-caliber weapons may be doing to the brains of our operators, breachers, and instructors.

You're going to hear from a researcher who was in the room in 2008 when the military first put a name to this problem, from a former operator who is living with the consequences right now, from a father who lost his son, a decorated Navy SEAL, to a blast-related brain injury, from one of the world's leading traumatic brain injury physicians at Harvard Medical School, and from a neuroscientist who works directly with tactical teams on how to do something about it. This episode has been five years in the making and it may be one of the most important things we've ever discussed. So, let's dig into it.

My name is Jon Becker. For the past four decades, I've dedicated my life to protecting tactical operators. During this time, I've worked with many of the world's top law enforcement and military units. As a result, I've had the privilege of working with the amazing leaders who take teams into the world's most dangerous situations.

The goal of this podcast is to share their stories in hopes of making us all better leaders, better thinkers, and better people.

Welcome to The Debrief!

Jon Becker: In 2023, New York Times investigative reporter Dave Philipps published a series of articles that caused a huge uproar in the defense and special operations community. Philipps had been investigating what was happening to the brains of American artillery crews, breachers, and special operators, and other people whose jobs have significant exposure to overpressure. What he found was deeply disturbing. The repeated blast waves from firing artillery rounds, breaching charges, and large-caliber rifles, were causing microscopic damage to their brains. Damage that looked nothing like a traditional concussion that showed up on no standard scan was frequently being misdiagnosed as PTSD or depression and was causing massive harm to the victims, including driving some of them to take their own lives. His 2023 series was a finalist for a Pulitzer Prize. His 2024 follow-up went even further by documenting that Navy SEALs and Top Gun pilots were among the hardest hit and that in some cases the Department of Defense had actively attempted to suppress the research data. That reporting had real consequences. In December 2024, as part of the National Defense Authorization Act, Congress passed the Blast Overpressure Safety Act, mandating every branch of the military to track blast exposure and design safer weapons.

The Pentagon began requiring baseline brain scans for all new recruits. 36,000 had already been scanned by the end of 2024. The DoD is now all over this. Massive research projects are underway. Special Operations Command leadership has made this a stated priority. A new medical classification code was created in the World Health Organization's International Classification of Diseases specifically to document repetitive blast exposure injuries. All of that happened in essentially two years. But this didn't come out of nowhere. I've been watching this build for five years. Long before it was on the front page of the Times, researchers were quietly accumulating data. Operators were silently experiencing symptoms that they couldn't explain, and families were losing people they couldn't save. Journalism brought it into public view. Science and suffering had been there for a long time.

My goal today is to give you some context on this problem, a little bit of the science, and most importantly, a potential framework of what you can actually do about it because the research will take years to fully resolve. The definitive answers are not coming next month, and in the meantime, your teams are absorbing exposure right now.

Before I get into the people and the science, I want to share the lens through which I've been looking at this problem for the past few years. It reminds me of the arguments that surrounded cigarette smoking before we officially decided it caused cancer.

In the 1950s, we saw the first serious studies suggesting that smokers were developing lung cancer at dramatically higher rates than non-smokers. There was a very strong correlation, but no definitive proof of mechanism. Then over the decades that followed, the evidence kept mounting, but the industry disputed it. The lawsuits failed and meaningful action never quite arrived with the urgency the data warranted. By the time we really did something, the master settlement agreement in November of 1998, when 46 states finally held the tobacco industry accountable for $206 billion in damages, it had been 48 years after those first studies. In the meantime, people kept smoking -- some of them thinking it was fine, many of them getting lung cancer.

In my Lessons Learned column in Tactical Edge, Josh Watford and I wrote, "The correlation doesn't mean causation, but it always precedes it. Every time we establish that something causes harm, there is always a period of time where the correlation is undeniable. The direction of the data is clear and the responsible people in the room say we need to act even without the final answer. In my opinion, we're in that period right now with blast exposure and brain injury. It's not time to panic. It's not time to abandon the tools that make teams effective because these tools save lives and nobody should be arguing to stop their use. But it is time to be smarter about how we use them. Perhaps put differently, don't smoke more than you must. Smoke the most filtered cigarettes you can find and don't chain smoke, but instead give your body time between cigarettes to heal. That's the prevention framework I'm seeing develop from all of the experts I've been talking to. Reduce how often you take the exposure, mitigate the damaging effects when you do, and recover before you take more exposure.

Okay, let's start at the beginning. At the moment, this problem was first formally recognized in a room full of scientists from five different countries. Gary Kamimori spent a decade at the Walter Reed Army Institute of Research studying blast exposure in operational troops. In 2008, he was part of a meeting that changed the direction of his research for the next 10 years.

Gary Kamimori: My name is Gary Kamimori. I am a biomedical researcher, recently retired from the Walter Reed Army Institute of Research. In 2008 at a meeting of the Five Nations Accord, which is the U.S., U.K., Canada, New Zealand, and Australia. It's similar to the NATO alliance. I represented an occupational medicine group where the New Zealand representative brought to the meeting that her operators were complaining of symptoms following explosive breaching training. At the same time, members of the U.S. medical community and the Canadian community expressed that their personnel had been complaining of the same symptom complex. The New Zealanders had given the term “Breacher's Brain” since it occurred at the end of a day of explosive breacher training. The symptom complex included headaches at the end of the day, dizziness and nausea, short-term memory issues, poor sleep the night of exposure, and all of these symptoms were gone by the next morning. So, they were transient in nature.

Jon Becker: The research that followed that meeting would prove that it was the instructors, the people with the most repetitive exposure, who showed the effects most clearly.

Gary Kamimori: The U.S. Marine Corps Method of Entry School in Quantico, Virginia was hosting a study looking at the breacher training program. The question from the commandant was, is is what we're doing in that training course safe for the students? They did a lot of tests to these guys at the beginning and end of every day for two weeks. What they found was interesting was that the students were really not affected by the breacher training. But a couple of the instructors who participated actually showed a change and that pushed us to believe that it was the additive effects of a lot of exposures affecting the instructors as opposed to the very acute exposure affecting the students.

From that point we were able to get a population of military personnel in New Zealand who were going to enter breacher training.

Jon Becker: That finding, that cumulative exposure is what creates the problem sits at the center of everything we're going to talk about today. And nobody I've spoken with understands it more personally than Eric Patrick. Eric Patrick spent years exposing himself to exactly what Gary Kamimori was describing and he had no idea.

Eric Patrick: Hello, I'm Eric Patrick. I'm from the Chicagoland area. I'm a retired disabled police officer. I started my career in 1993 in two cities just outside of Chicago, Illinois and Indiana. In 1998, I went to the railroad police. In 1998 I was working in the Chicagoland area, predominantly theft from the rails.

After 9/11 hit, our government and the railroads all met and said that we need more policing. The government says we can't give you more policing, but we can give you more funds and special teams. This evolved into guys going into a HIDTA program working with the federal agencies mostly FBI counterterrorism. I applied for the tactical team as a dog handler. We started in 2004 training and continued doing missions throughout the United States. In 2005 I trained with the German Polizei. In 2006 they came here to continue our training. In 2008, we continued our training in Germany and Austria.

The training was predominantly interdiction and also terrorism with the rails, any kind of transportation, buses, trains, and planes. So, we specialized in entries with this program. It evolved into training other departments and I think it was the last when I left over 600 to 700 different SWAT teams in the United States that we trained. The training was usually 3 to 4 days and we gave them a whole look at different rail systems. I was one of the instructors and role players. In 2005 we started using flashbangs for realism in the training train we used and we were inside the train sleeper cars, double stack cars, different types of rail system that we would have and we would use FX ammunition rounds that had little projectiles. They would use full flashbangs on us and while we were inside the rail system it was normal for all my teammates for us to have ibuprofen in our cars everybody would have headaches.

My first time I really started seeing issues I remember was around 2006 to 2007 and that was I was always tired but in a weird sense so I would get up as a dog handler, and say at 6:00 or 7:00 in the morning you go to work in Chicago. Well, I would go run with the dog and I would run three, say three or four miles with the dog. I'd come back and I would take a shower and I wasn't just tired. I was so tired I had to lay down and go to bed. So, this happened for a couple weeks. I went to the doctor. He checked me and even in the notes you'd see, “Did you fall down? Did you get in a car accident? Did you hit your head?” So the doctor at the time was even trying like these are signs of a head injury but no I don't have a head injury. No, I didn't get into an accident. I wasn't in a fight. I didn't fall down. Didn't hit my head. Nothing was there.

Then, which was interesting, it got better. Kind of went away. Well, this was in the beginning of the year and we didn't train with other SWAT teams because of weather problems in December and January. If you go anywhere in the northern parts of the states, it is cold, and even in the southern parts of the states it is bad. So, it was kind of hard because we were outside a lot and there's no heat. So, we wouldn't do any training as a team in the latter months, December, January, even February. In March, we would start right back up again. So we would probably start in March, April and we would start training again. Lo and behold, the symptoms would come back of fatigue and being tired all the time.

Jon Becker: Talk to me about the kind of long-term effects on your memory that you're still experiencing.

Eric Patrick: If it's not there, it's not there. My neurologist told me that it is like a file cabinet, and information is stored in the file cabinet, but this information is going to the file cabinet, but the door is not open. So, it's getting there, but it's not staying there. So, that's why it's not there. And I even caught watching a Cinderella movie years later with my daughters at the movie theater. I had young stepdaughters at the time and we decided to watch it years later on TV and there was about 45 minutes of the movie in the middle of the movie that I don't remember. It's just it's brand new and that happens. That's how I caught it even today. That's how I catch it on a daily basis. “Oh, what? I don't remember that but I know I did it and it's not there. The memories just gone, and it's wiped away.” So that's a struggle that we have every day.

Jon Becker: Did you notice anything like mood symptoms? Were you having problems with anger or with frustration or…?

Eric Patrick: Irritability, I call it irrational irritability where I'm getting angry at things that I shouldn't logically get angry at like my friend scratching his nose while I'm talking to him. That would be something I'm getting angry. It's a real feeling. But if I take a step back and look at it, why would I get mad at that, you know? But at the moment, it's really there. So, anybody's suffering from a brain injury and we're talking blast level is getting this and they don't realize that this is happening to them because they just feel really angry. There is a real reason why he's getting angry.

I used to start my talk and I did it in LA and I don't know if you ever watched the Avengers movies where Dr. Banner comes riding up on a motorcycle in New York to help the Avengers. And Captain America says, "Good of you to show up, Dr. Banner." So now Dr. Banner is going to become the Hulk. And he's going to go fight the bad guys. Captain America says, "Hey, Dr. Banner, this may be a good time to get angry." And he turns and smiles at him. He says, "That's the secret, Captain. I'm always angry." And he turns green and he starts fighting the bad guys. To this day that's exactly what I experience now. I just have to know it's there. I have to take a step back and say, "Why am I getting angry? Is this something logical to get angry?"

This nurse practitioner that interviewed me, he asked me one question that all the doctors in the beginning failed to ask, “Were you around or working with any explosives?” And backing up the guy that just tested me, I said he had that on the question. And he asked that too. And I said, "Yes, I did." And he said, "What?" And I said, "Predominantly flashbangs." He goes, right after not even researching it and how close I was to it, how many I was around, what the environment was. Was I indoors, outdoors, was it metal, concrete, the things we talk about, he said, "Oh, that can't be it." That's how quickly that question was. Well, the new psychiatrist, the nurse practitioner, asked me that question. That one question turned into 45 minutes of talking trying to figure out and he's typing on his computer what kind of flashbang. He types it in and turns the computer around. I said, “That one”. “How many?” And it just kept spiraling into it.

When he was younger, he worked with I think the VA or the military. So he was a little bit versed in this and knew a little bit about blast force trauma to the brain. And he told me about if you look at the old shell shock, these old pictures of World War II guys and they're with artillery and they just had this blank stare on their face just this looking off to nowhere stare. He said, “I think you have depression”, he put me on an antidepressant but I think you have a brain injury. Then I went back to my doctor and that's when he said this is what I do and he started the ball rolling with the impact study of how bad I was. Then I went to a neurologist and the neurologist said, "Let's get this report. Let's get you to an endocrinologist." Everything just seemed to happen really fast from like 2016 and 2017. Within that year, I started seeing a crapload of doctors.

Jon Becker: If you had an opportunity to sit down with young operators today, what would you tell them about low-level blast?

Eric Patrick: Train better. Train smarter. They're so new and I always equate this to the NFL. They're training differently now than they did when you and I were younger and watching guys hit themselves. So, you have to train smarter, like in football. There's less contact. So For this, the same analogy is that you set your environment up. Don't use full flashbangs in your training. I'm sure you have to use them. They do great, but don't train with them. Use blankets that are out there, suppressors. There's so much information out there that you can help yourself, but train smarter with.

I honestly, Jon, no doubt in my mind, if if we had this type of information, I don't think I'd be sitting here talking to you.

My daughter got married and I was not a SWAT operator anymore, but I was just out of it and I don't remember that she got married. I know where she got married. I know where the reception was and I've seen the pictures, but that's the only memory that I have. I created my own memory from pictures, not from being there. So, I don't remember dancing with her. I don't remember her saying I do. I don't remember anything. Everything is from a memory from a picture.

Jon Becker: Eric absorbed that damage in training over years without knowing. What we're going to hear next is what that kind of damage can eventually lead to and the price a seal and his family paid because we didn't understand this. Frank Larkin has spent 4five years protecting people in the military, in law enforcement, and in government. In April of 2017, his world was turned upside down.

Frank Larkin: I lost my Navy SEAL son who died from his combat injuries. He took his life one day. After multiple combat tours, he started exhibiting a lot of what we see in our veterans. I ultimately came to find out that he had a severe level of undiagnosed brain injury at the microscopic level from blast exposure. He was a sniper and a breacher along with being a special operations medic, very smart kid, highly decorated, highly revered operator. And that put me on this path to get into the nonprofit space to help veterans and first responders and try to understand this threat that is truly challenging brain health and also the lifestyle of many of the folks that raise the right hand do special things for us as a society to keep us safe, secure.

My son Ryan started exhibiting what we would define or characterize as behavior that was not him following his third deployment. He had done two prior deployments to Iraq. His third deployment was to Afghanistan. It was back-to-back with his Iraq deployment which put him into a combat zone for almost a year. When he came home from that we started to see changes in him. He stopped smiling. He became shortfused. Complained that he couldn't sleep and then when he did he was having nightmares. He was a kid that was very intelligent, and had a tremendous ability to abstract. He very often used to plan missions because he could see second- and third-order effects and after his third deployment again you're balancing the fact that here you have a Navy SEAL who's a seasoned combat operator are these changes because he's maturing he's seen action or is there something going on. So we were in the face of not knowing exactly what was taking place.

Following his third deployment, he went to SEAL sniper school where he was firing high-caliber weapons, the 50-cal and other weapons with very intimate contact and high volume of fire. Very often he complained of having migraines after a day on the range with the 50-caliber and sometimes having nosebleeds. So his symptom presentation was progressive and yet he was able to do his job. He loved being a SEAL and he moved on to his fourth deployment.

At the time of his death, what we found on his computer was endless research papers and articles where he was looking into brain trauma and he was researching the side effects of these medications that they were putting him on. He knew something was wrong. I remember him telling me, John, that he said, "Dad, dad, something's wrong with my head. Nobody's listening to me." We were sitting around a fire one night. He felt that he had let his brothers down by leaving the Navy. He was their doc. He was the corpsman, the medic that they depended on and he felt a great obligation to take care of them. and they never went outside the wire unless he went with them. And it didn't matter how bad he felt, he was going with them. And he says to me, "Uh, hey, I'm banged up inside and I'm not going to live long. I just know it." He says, "If anything ever happens to me, I want you to donate my body to traumatic brain injury research, breacher syndrome research."

On a horrible Sunday morning of April 23rd, 2017, we came home from an overnight trip to we were out of town and something wasn't right. As soon as we pulled in the driveway and I found that he had taken his life in the basement of our home. He said he'd never do it. He said that's not the way I'm going to go, but I know this was eating at him. He was dressed in a SEAL Team 7 t-shirt, and wearing a pair of red-and-white board shorts and had illuminated a shadow box that had all his medals, ribbons and insignias next to him. I'll tell you in the 4five years that I've been in public service both in the military and my 35 year career in law enforcement and intelligence. I spent most of my adult life rescuing other people and in the end I couldn't rescue my own son. I carry that burden. The only way I can deal with it is by doing what we're doing right now is talking about it and trying to inform people that we got to get to the bottom of this. We can't lose anymore. I don't want anybody else to walk this path of pain. He knew what he was doing. He wasn't taking the easy way out. He wanted to prove that something was wrong. And he was right. He died from his combat injuries. He died training for combat. He just didn't die right away.

Jon Becker: Ryan Larkin knew something was wrong with his brain. He said it out loud. He researched it himself. He told his father to donate his brain to science. Interestingly, for many of us, our first exposure to traumatic brain injury came through a very different industry, football. In 2013, Junior Seau, a Hall of Fame linebacker who played for the San Diego Chargers for most of his career, shot himself in the chest. He was 43. Before he died, he reportedly asked his family to donate his brain to TBI research. When the researchers looked, they found chronic traumatic encephalopathy or CTE. Now, CTE and blast-related mTBI are not the same condition. I want to be clear about that. CTE comes from repeated physical impact, the kind that happens when two football players collide thousands of times over a career. The damage appears in a different part of the brain through a different mechanism than what Gary Kamimori and the researchers we'll hear from today are studying. Gary actually explained to me how these things sit at the same scale but are distinct. But what the Seau case gave us was something important, a moment of public awareness. For the first time, a lot of people understood that brain injury could change who a person was, their personality, their moods, their ability to function in ways that were invisible until it was too late. That's the connection. The mechanism is different, but the warning is the same. Which brings me to Dr. Daniel Daneshvar. Dan was one of the first researchers in the world to specifically study CTE. He now works with both NFL players and special operators. He's probably better positioned than anyone I've spoken with to explain what is happening inside the brain and why blast exposure is its own distinct and serious problem.

Dr. Daniel Daneshvar: I started doing this work really out of undergrad when I was really concerned about brain diseases. Honestly, neurodegenerative disease scares the hell out of me. This idea of losing who you are is terrifying. But I was also an athlete in high school and in college. And so I started learning more about the long-term effects that repeated head impacts can have and the possibility that those could increase the risk of problems later in life. And so that's why I started doing this research. And that was 17, 18 years ago.

Jon Becker: So talk to me like your area of study now, the area that you're practicing in is kind of traumatic brain injury as a result of kind of impact and low-level blast and all these kinds of things, right?

Dr. Daniel Daneshvar: Yeah. I'm basically trying to understand all the different things that can happen after you repeatedly hit your head. And some of those are neurodegenerative processes like CTE, chronic traumatic encephalopathy is one of them. Lou Gehrig's disease or ALS is another one. We're learning about all kinds of other blast-associated ones as well, but it's also changes in your personality and your memory and your behavior that's not necessarily neurodegenerative-related.

Jon Becker: Yeah. I mean, one of the common complaints with low-level blast is personality change, becoming short-tempered. like all of a sudden he just didn't smile anymore and he was unhappy. That and that's kind of what you're finding.

Dr. Daniel Daneshvar: That's exactly right. What we're realizing is that the parts of the brain that are most responsible for your personality, for who you are, are also parts of the brain that tend to be most lined up along the ridges of the front of your brain. Whenever you receive head impacts, some of those are the areas that are most affected. You see that not only for repeated traumatic brain injury, but for decades, we've known that this can happen after moderate or severe brain injury. These are the kinds of brain injuries that result in brain bleeds and skull fractures. Now, we're increasingly realizing though that those repeated brain injuries, they can add up and cause problems, too.

Jon Becker: Interesting. So, walk me through what happens when we hit our head, whether it's we're hit in a football game or, you know, we have a blast move through our brain. What is going on inside of our skull?

Dr. Daniel Daneshvar: Yeah. Well, our brain is kind of Jell-O-like in terms of consistency. If you were to put a brain in your hand, it would move and feel like jello. When an impact hits the hard skull, that impact is transmitted through the fluid of the brain and into this Jell-O-like surface. And so that causes a direct impact to the brain tissue, but it also causes different levels of impact all through the brain because unlike a bowl of Jell-O, your brain has a lot of different types of tissue in it. So for example, the blood vessels in the brain, they're a little stiffer. I would think of them as more like uncooked spaghetti. So if you had a bowl of Jell-O and you were to hit it, it would jiggle and then afterward, if you looked at it, you wouldn't be able to tell that you'd hit it, right? It would look about the same. But now, if I were to put uncooked spaghetti into that and then I were to hit it, the Jell-O would move and the spaghetti would move, but they both move a little differently. When they moved differently as a result, when it was all done, you could look at it and you might see small cracks in the Jell-O around where those spaghetti are, small cracks in the brain tissue around where the blood vessels are. That's what we're seeing happens after repeated brain injuries and after repeated blast exposures because things are absorbed and reflected and transmitted in the brain tissue in different ways based on the types of tissues involved.

Jon Becker: Yeah. Yeah, and I think one of the things you said that's important is that it is transmitting through the skull, right? Your ear and eye protection is not going to stop this.

Dr. Daniel Daneshvar: That's absolutely right. It's reflecting off of the skull surface. And that's what makes blast different than say an average football exposure where if someone gets hit in the head during a football game, that is a it can be a really hard impact, but that hard impact is transmitted and then it might vibrate back and forth a little bit, but then it's done. Whereas when you're talking about a blast field, that blast wave is propagating through all the tissues, bouncing around surfaces in the environment and bouncing around those same surfaces inside your brain. So that same impact might actually translate into a lot more than what the force itself would suggest.

Jon Becker: I guess if it happens once and you give it time to recover, your brain can heal itself most of the time.

Dr. Daniel Daneshvar: Yeah. In the vast majority of cases, single impacts don't cause long-term issues. Your brain is resilient and can heal. The problem comes with those two factors you just mentioned. It's when they're repeated and when they're close together.

What we're learning, and what we've known from animal studies for over three decades at this point is that there's a window of vulnerability where if you get hit in the head while your brain is still healing, then that can cause more problems. It's like if you have a bum ankle, right? If you turn your ankle and your ATFL, your ligament, your ankle is sprained not to put weight on that because if you tried to run on it, it would require less impact to further exacerbate that injury to cause a lot of problems. But the difference between your ankle and your brain is that your ankle has special nerve endings that tell you there's pain, tell you there's an injury. Your brain is full of nerves, but it doesn't have those kinds of nerve endings. It doesn't have the ability to say, "There's an injury here. We need time to rest. We need time to recover." So, the only way we know about that is when the brain tissue just isn't working the way it's supposed to. And that is what the concussion symptoms, what brain blast injury symptoms, what all these changes we're seeing are. It's the brain not functioning the way it's supposed to.

Jon Becker: Interesting. So, yeah, I mean, because there's no pain receptors in the brain, right? So you like your brain could be really unhappy and the only way it's going to let is your vision is blurry or you have a headache or you can't remember things or you're going to get angry more easily or some kind of secondary symptom that if you're paying attention which most of us aren't if you're paying attention is going to say there's a problem. But if you're not paying attention your brain has no real mechanism to warn you that you've injured it.

Dr. Daniel Daneshvar: Yeah you're absolutely right. Your brain itself doesn't have those kinds of pain nerve endings. The area around the brain does. And so when they're doing nerve surgeries, they'll lidocaine up the areas around and area of the skull they cut off and the area around the brain itself. But once you can cut into the brain tissue, you don't actually need anesthetic for that. And that's because the brain doesn't have those kinds of nerve endings, that tissue. In fact, that's important because in some cases when they do neurosurgeries, they want to keep you awake so they can talk to you and figure out-- they'll numb up an area and see if that area is something that's critical for say your ability to speak or your ability to do something that's important to you. They want to make sure that when they're doing the surgery, they're not cutting through anything important.

Jon Becker: I think as a novice as somebody that doesn't understand medicine, I think we have this perception that we're all kind of exactly the same, right? Like everybody's brain is kind of the same and everybody's built kind of the same. Some are tall, some are small, some are short, some are tall, some are fat, and some are skinny. But I think we have this idea that the anatomy is the same. And that's not true, is it?

Dr. Daniel Daneshvar: Yeah, that's absolutely not true. We used to think that there was this idea that different parts of the brain were responsible for different functions completely. We know I mean increasingly that that's not even true. Some parts of the brain might generally specialize in certain things, but your brain might be different than my brain in terms of where you process some of your language or where you process some of your vision or and so all of those differences are things that we need to take into account because just like everyone's brain is different, everyone's response to a brain impact is different and everyone's possible brain injury is different. So we have to understand all of those to understand any one specific brain impact.

Jon Becker: Yeah. Even if you and I are exposed to the same thing, the effect on us is going to be different. And the way like those secondary symptoms may manifest completely differently. I may get angry and you may get tired.

Dr. Daniel Daneshvar: And that's part of the problem because it's not only that the impact itself might be the same. So, for example, when we're talking about blast force, if there was a blast and we're the exact same distance from it, based on the room and the situation and maybe the table or other factors in this area, the propagation, the force that your brain feels is going to be different than the force that my brain feels. And then we add on the factors that you just mentioned, which is that our brains might be different, too. And then we add on the fact that even if the same area of our brain that's responsible for the same functioning might be injured, we have 86 billion neurons in our brain. So if you have damage to say 100,000 of them, that's like 0.00001 of your brain tissue. So your 100,000 neurons that got damaged in that same region of the brain might be different from my 100,000 neurons in my part of my brain.

Jon Becker: Oh. Yeah. So like I might have a headache or not remember my seventh grade teacher and you might be totally fine.

Dr. Daniel Daneshvar: Yeah. My seventh grade teacher part of my brain might be an entirely different part of my brain.

Jon Becker: So one of the things that that is kind of a topic is there's been a lot of equation aligning low-level blast with normal concussion and what happens in football and CTE. Can you kind of dissect those for me and like explain how this is different?

Dr. Daniel Daneshvar: Yeah, so we in many ways are piggybacking off of what we learn from sports athletes and those repetitive head impacts to try to advance the science about head impacts overall. But we know they're very different kinds of head impacts. We know that the types of head impacts, the forces associated with a football impact are very different than the percussive wave that is experienced by a service person or really anyone exposed to a blast. So CTE then is a neurodegenerative disease like Alzheimer's or Parkinson's, one of these other neurodegenerative processes where there's a specific kind of protein in the brain that basically causes brain cells to die and that protein can be present in Alzheimer's disease but it's also present in CTE, and that can cause some of the problems with memory and other problems that you see in CTE. But that might not be the exact same process. In fact, it almost certainly isn't the exact same process causing problems that we see in our servicemen and women.

The difference is what we end up seeing is more problems around the blood vessels and more problems at the spa, the area between the outside of the brain and the inside of the brain in response to blast. It's because all of those different cells are responding differently to the force going through the brain.

Jon Becker: Which is going through a really high rate of speed, too, right? It's not just it's not just that it's moving the brain. It's moving the brain really fast.

Dr. Daniel Daneshvar: We've done studies where my colleagues have put an animal at the end of a long blast tube and fired the blast and it looks like the animal's head, the mouse's head for example wiggles back and forth. But then when you look at it at high frame rate cameras, that back and forth movement actually looks like a hundred back and forth movements because that wave is going back and forth so quickly.

Jon Becker: Yeah, because you have the incident wave and then the suction wave that's following it. So you're pushing it back. It's the same thing as what breaks a window in an explosion. It's usually not the push in; it's the pull out that does it. So you're not only getting exposed to the 3 PSI overpressure, but you're then getting hit with the suction wave that's falling behind it. So that might be a 5 PSI transition that's now rattling you at an extremely high rate of speed.

Dr. Daniel Daneshvar: And if it was just the three and then the five back and forth, that'd be one thing. But it's the three and then the five and then a two and a half and then a four and then it's going back and forth and back and forth all within one single blast wave.

Jon Becker: So now you take that you inflict an injury and if that's allowed to recover, maybe no big deal. If you look at an average training day for a SWAT team that's doing breaching training or doing flashbang training, they're being exposed to that blast maybe 20 or 25, 30, 40 times in a day. Now you're repeating that trauma to the brain. Each one of which is different, right? It's not that you're not repeating exactly the same trauma because your head's in a different position and the wave reflects, but you're repeating that trauma repeatedly over this short period of time, and not allowing the brain to fix itself.

Dr. Daniel Daneshvar: That's exactly right. our brain is remarkable and able to fix itself if given time. Not only do we often have training days with repeated blasts in a day, but then there isn't real thought given to what the next exercise they might be training would be. So for example, you might go from training to then jump school, rattling your head by falling hard landings and hard openings and not giving your brain the time to rest from the first activity or the next activity or the activity after that. You might then start shooting Carl Gustafs and it ends up becoming an additive exposure where each additional thing adds up without any time for recovery, without any time for rest, and it's like you're running on that bum ankle and it's going to break.

Jon Becker: Well, and you pointed out an interesting point there, which is it's not just the blast exposure. It's combatives. It's jiu-jitsu. It's it's jump school. Anything that is subjecting the brain to shock is going to continue to perpetuate this injury. You're absolutely right.

Dr. Daniel Daneshvar: And on top of that, many folks that are going into this type of space, they're not coming with a full gas tank in terms of blast exposure or head impact exposure. Many of them were contact sport athletes. Yeah. well before they even enlisted. And so there's that other aspect that also needs to be taken into account. Your brain is the sum of your entire life's experience. If you use a smoking analogy, you might have smoked some in high school. And then you have to take that into account when you're considering how much you're smoking later in life.

Jon Becker: Yeah. I like the smoking analogy because I think it's very on point, right? On the one hand when in the 1950s, we knew smoking probably caused cancer, but we couldn't figure out how much was safe and what was safe. And we couldn't really establish true causation. We could correlate it. Those two things happen frequently. That doesn't mean one causes the other one. Talk to me a little bit about that with what kind of what you're finding with traumatic brain injury.

Dr. Daniel Daneshvar: Yeah. One of the things that frustrates me when it comes to our understanding of traumatic brain injury and the long-term effects is this idea of like a safe threshold. And in the ' 50s, I think a lot of the early science was centered on understanding what was the safe level of cigarette smoking, whether filters were safe or what were the factors that made cigarettes more or less safe. But we know about cigarettes now. And we know there isn't a safe level of smoking. Just like about head impacts, there isn't a safe threshold for PSI or a safe threshold for repeated head impact exposures. What we know is that more is riskier. There isn't a number where after this magical number, suddenly you're going to have problems. Everything's about risk. But we understand risk in a lot of other aspects of our life. If you have an exposure to cigarette smoking, for example, it's not like on your 50th cigarette, you're suddenly going to get lung cancer. We all know the 94 year old grandmas who smoke 150 pack years of smoking and are healthy as an ox and still cooking. Risk doesn't mean certainty. And so that's what we're also learning is the case for brain injury.

Jon Becker: I mean you're working with everybody from NFL athletes to SOF warriors. Your practice is kind of spanning. I would call it like the top tier of a variety of professions that are affected by this. How are you guiding them in how they should view exposure?

Dr. Daniel Daneshvar: Yeah. What I tell them is for the most part we can't do anything about the exposure you experienced in the past. But what we can do is implement common-sense interventions to decrease your future exposure if you're still an active football player or if you're still a member of the SOF community. So that's one thing that we can do is implement things like better equipment like taking breaks between exposures like eliminating the types of exposures in training and in practice that can be eliminated. For example, in football, because there's helmet sensor data, we know that about 70% of the head impacts that occur in football occur in practices.

Jon Becker: Yeah.

Dr. Daniel Daneshvar: Right. So, we can eliminate those without changing anything. So, by implementing these common-sense things to reduce the cumulative amount of head impacts you're getting, you're improving your mental health and your cognitive health and your long-term neurologic health. But then what we can also do is try to implement treatments to separate the extent to which your brain health influences you day-to-day. And what I mean by that is that your brain is responsible for everything you do, but it's not a one-in, one-out process. You can have brain damage to one area of the brain, but your brain can work around that without you noticing it at all.

So if I can treat people and increase what's called their “Cognitive Reserve”, increase the ability of their brain to route around problems and they never experience problems or the problems they experience are substantially lessened, then I've effectively treated their brain even if I can't actually treat the underlying structural issues.

Jon Becker: Interesting. So what like when you're doing that, how are you doing there? What kind of exercises are they doing? Is this something people can do preventatively?

Dr. Daniel Daneshvar: Yeah. So the interventions that I do are very personalized based on that patient's life issues but for the most part there are some common themes that are consistent for a lot of these patients. So for example sleep disorders are really common both in my elite athletes and in my SOF personnel. So for example sleep issues like sleep apnea, you can imagine that being the case for your average offensive lineman 400 pound guy because your neck size is a direct relationship to your risk of sleep apnea. So that's why some of them might be having sleep problems. Similarly in my SOF personnel nightmares are often a cause for sleep issues but both of them have disordered sleep. What we know from a whole huge body of literature is that there are four stages of sleep. In one of the stages of non-REM sleep, it's called “Deep Sleep”. That stage of sleep is responsible for clearing out all of the toxic metabolic products that build up throughout the day in your brain.

So most of us don't realize that your brain is about 7% of your body's mass, but it uses over 20% of your body's energy. So it's one of the most metabolically active tissues in your body per gram. It uses more energy than even your muscle when you're working out your hardest. And just like a car, if you put a lot of gas in, it's going to have a lot of exhaust. The brain is constantly producing that exhaust. And that exhaust clears in deep sleep. So deep sleep is critically important. And that's what gets disrupted when you have disordered sleep, when you have sleep apnea, when you have nightmares. We know that when you have that disruption in deep sleep, you have higher rates of Alzheimer's disease, you get higher rates of dementia later in life, you get higher rates of Parkinson's. That disrupts your ability of your brain to be resilient. So that's one of one example of something I might treat for you.

Jon Becker: Yeah. So you've interrupted the maintenance cycle for your brain basically. If you think about guys that are working nights they're getting up very early in the morning to go serve warrants or like in the case of a SOF warrior, they're working at night. They're doing high adrenaline, high energy things, drinking a ton of energy drinks. Then trying to fall asleep and not sleeping well. You can see where this just starts to become like this destructive cycle where you're not sleeping and you're injuring your brain and your brain doesn't have time to fix itself and then you're reinjuring your brain and you can see how this becomes kind of a downward spiral.

Dr. Daniel Daneshvar: That's exactly right. When the brain is injured, it fires more than it normally would. Basically what's happened is the brain cells themselves get stretched and they end up being unable to control their firing. So what happens then is it uses more energy. Your brain is even more active and needs more time to recover than it normally would. If you're taking away someone's sleep on top of that, then you're going to compound their problems.

Jon Becker: So when you're working with patients with this, what are you doing to help them sleep better? What are the things that you're telling them to pay attention to?

Dr. Daniel Daneshvar: So the very first thing I do is to get a sleep study on anyone who's having these kinds of issues to get a sense of whether there's a specific target for their sleep. If it's because they're for example someone with sleep apnea, well then there are multiple different interventions from CPAP to dental appliances to other things that can be done to improve someone's sleep. They could have restless leg syndrome. There's medication for that. They could have disordered sleep due to nightmares. There's medication for that too. There's obviously cognitive behavioral therapy and other things that might help individuals fall asleep. There are things that we can do to improve people's circadian rhythm if they constantly have to move from nights to days and back and forth. There are all these kinds of things that we can do and that's why it's really individualized and holistic.

Jon Becker: But it's also like I think we are learning in the last 10 or 1five years how absolutely critical sleep is and the nature of this profession and sleep don't exactly go hand in hand I don't think people take sleep seriously enough.

Dr. Daniel Daneshvar: Yeah, you're absolutely right and I think that's one of those low-hanging fruit things that we don't think is serious. I mean there's a tough-it-out mentality even for me and I certainly wasn't in this community but when I was in med school right there was a, “Oh you slept 2 hours last night I slept 30 minutes last night”. There's a toughness associated with not taking care of your body and I think what we increasingly need to realize is that sleep health is brain health just like heart health is brain health and pain health is brain health. Your brain affects the body and your body affects the brain and all of these things are important for how you're going to be doing later in life.

Jon Becker: So if you're advising a team, if I brought you into a SWAT team and said, "Okay, how does this team -- I mean, they can't eliminate this risk? How do they mitigate it? What are your favorite kind of best practices for a SWAT team or a SOF community like these are the things you guys need to be thinking about doing?"

Dr. Daniel Daneshvar: Yeah. So I would never presume to be able to give specific recommendations because I've never lived that life and been asked to do that. And you're absolutely right in that we can't eliminate these exposures nor do we really want to. We need some people to be willing and able to do this. What we can do is make sure it's as safe as possible. And so those safety things we can do are decreasing the total exposures cumulatively. What that means is to decrease the unnecessary exposures. Space them out to the extent possible and listen to your body because there's no toughness in toughing it out from a brain injury. You don't have the same kind of pain nerve endings to feel pain like you do in your ankle that you do in your head. When your brain is injured, when you're not feeling right, when you're not sleeping right, when you're behaving differently than you normally would, when you're really depressed, when you have double vision or horrible headaches, all of those are indications that your brain isn't working the way it's supposed to. Those are indications that you might need a break.

Jon Becker: It's funny because I think anybody in this community that rolled their ankle would go see an orthopedic surgeon and get their ankle looked at. And yet, when you look at brain health and you look at emotional health, somehow we have stigmatized both of those so that it's like, well I mean, yeah, you're tired, but I know the doctor, you've been up for 3 days, but you're still going to work for another 12 hours. We don't stop to go, “Well, the doctor that hasn't slept for 3 days isn't going to make good decisions”.

Dr. Daniel Daneshvar: Yeah. They've done research studies where they've kept people up for 24 hours and then they had them drive a car and they drove like they were legally drunk. Yeah. And so when you're making decisions and you're legally drunk, you never take a shot before you go out and start shooting in the same way that you shouldn't be staying up for 24 hours straight and then expected to perform at an elite level.

Jon Becker: Yeah. So, we're going to reduce overall exposure. We're going to let ourselves recover between taking symptoms seriously, obviously. What are some other things that you think teams need to be at least thinking about or paying attention to?

Dr. Daniel Daneshvar: I think that one answer if we know it's the cumulative force that matters, there is equipment and other things we can implement to decrease that cumulative force; especially in training where the environment is something we can control. That's something where they're going to have to practice. They want to make sure they execute perfectly when it matters. So, but there are factors in training that we can modify that don't take the realism out of the situation, but that make it safer and those are the kinds of things that we can implement.

Jon Becker: Give me some examples.

Dr. Daniel Daneshvar: So for example we know that a blast wave propagates and bounces and reflects off of all surfaces and environments. There are ways that we can mitigate those blast waves by putting different types of materials in the training environments that might decrease the amount of forces that are transmitted to the brain.

Jon Becker: Yeah. Softening walls, not training inside of concrete buildings putting rubber mats on floors. I think that that's a lot of where we need to get with this because it's complicated. It's scary. I mean, you guys don't even understand it. You do this for a living or an MD PhD teaching at Harvard and it and this is complicated to you. So you can see where an end user is going to look at this and go. It's too hard. I can't understand it. I think that a lot of what we need to be focusing on is simple rules of thumb. When do you think we're going to see an actual causal relationship? If you had to look into your crystal ball and say in x number of years, we're going to know what the causation is here, is that a one-year out thing? Is it a 20 year out thing? What is your gut on it?

Dr. Daniel Daneshvar: Well, so when it comes to cause, it's cause of what, right? Because there's a lot of different things that can happen after you get hit in the head. So is it the causal relationship between head impacts and say that one protein I mentioned for CTE like that at this point is pretty well established. But that's not the only thing that's going on. There's blood vessel damage that's happening and there's damage at the junction between different brain tissues that's going on. There are all these different things and we don't know which of those is most responsible for say a specific behavior change. And that's part of the complicated thing.

I joke that my PhD was the first PhD in world history to look at chronic traumatic encephalopathy, CTE, which is a disease that has been recognized since 1928. I jokingly say that my dissertation was about how getting hit in the head a lot is bad for you. So, we might not understand the details, the nitty-gritty, but that doesn't stop us from making decisions that get us 90% of the way there. I think honestly it's going to be a lifelong mission for me to really figure out every single detail and every avenue of this. That doesn't mean we don't know anything yet.

Jon Becker: Yeah. And I think it's the thing with the brain like we know that if you roll your ankle, you tear a tendon, tear a ligament, you can go to an orthopedic surgeon, he can put it back together, if you damage your knee, you get a knee replacement, or maybe you just limp for the rest of your life. You don't forget your kid's names. You don't kill yourself.

Dr. Daniel Daneshvar: Right. These things are complex and multifactorial. Just like our brains are all different, our genetic histories are all different. So our family’s history of dementia for example plays a role in our risk of dementia. Our family history of mental health illness plays a role in our likelihood of having mental issues. All these things were all complex and nothing has a single factor behind it. But we've got to understand the general trends to make sure that we can intervene and help people.

One of the things that I think is clear from the subtext here, but that is often confused is that a lot of people just think that concussions are the problem and that we need to regulate concussions. So concussions are a head impact that results in symptoms, things like blurry vision, double vision, that kind of stuff. But based on helmet sensor data in football players, they've looked at an average offensive lineman who gets a concussion and they've gone back and looked at his helmet sensor data and realized that for each concussion that that person had diagnosed, they had on average 341 head impacts that were of equal or greater force than the head impact that caused the concussion.

So, what we realize now is that all those hits matter regardless of whether we call them a concussion. All those blasts matter regardless of whether we're measuring them or what the PSI is. Everything is adding up and those are the things that are causing problems later in life.

Jon Becker: I mean, what you said there is actually terrifying because what that means is you had 341 head impacts. One of them produced enough symptoms that a doctor called it a concussion. that may just be that the other 340 affected part of your brain that you didn't produce symptoms for. And maybe you just forgot the name of your seventh grade math teacher.

Dr. Daniel Daneshvar: I think that's exactly right. Our brains are doing so many different things that we're aware of and that we're not aware of. And it's possible that an area of the brain was injured that we're just not aware of. We call that non-salient areas of the brain. I think that's probably what's happening. But so on the one hand, it's terrifying, right? in that we know that all these hits matter. On the other hand, it's also empowering because we know that we can eliminate a lot of these unnecessary hits and it's also reassuring because I often have patients who say I got one really bad concussion or I was in a car accident and this happened to me. Does that mean that I'm going to have CTE or that I'm going to have problems later in life? And we know it's not one head impact that's causing this. It's tens of thousands of head impacts. And so that makes it a lot of low-hanging fruit of things we can address. We can't always control the one-off, the IED that goes off in the car in front of you and causes a blast wave to you. Those single exposures are not things that we can control, but we can control the tens of thousands of other head impacts that occur throughout training and throughout life without fundamentally affecting our operational readiness.

Jon Becker: Well, in the case of a SWAT team, like 90% of their exposure is probably going to be in training. That's exactly right.

Dr. Daniel Daneshvar: Yeah.

Jon Becker: It's operationally it's not going to be that often that you're operationally exposed. So, in that sense, you do have kind of control over the majority of times. And I guess you don't know it's it's if your brain is like a tire, you don't know how many miles you have until until the tire wears out. like you might be 10,000 and I might be 40,000 before I end up with Parkinson's but you don't know that. So you got to just keep that number as low as it can possibly be.

Dr. Daniel Daneshvar: Yeah, you're absolutely right. We don't know how much gas we all have in our tank. and I don't know why I only have 10,000. You got 40,000.

Jon Becker: Because I'm a much thicker skull. Yeah, just ask my wife. I'm very hard-headed. I think one one other area I just want to kind of touch on is I think there's a notion and as as I was doing the research on this, I kind of naively assumed that a concussion was some magical criteria that you were going to do a blood test or you were going to do a scan and say, "Oh, well, you have these three biomarkers and so you have a concussion. And I think one of the things I found most troubling in my research is a concussion is you say I have a concussion because I have a collection of symptoms.

Dr. Daniel Daneshvar: You're exactly right. And that's one of the remarkable things when we're trying to come up with that blood test that you're referring to or any test to objectively say whether or not someone has a concussion. What we're finding is that none of these tests do that. One of the reasons I think that that might be the case is something you said earlier, which is that if you have one of those 341 head impacts that was of equal or greater force than the concussion, that could be causing an injury. And that could be causing an injury that the blood test is picking up. And then when we look at the blood test, we say the blood test, it doesn't show up when it shows up all these times when there's no concussion, but it could be really accurately telling us that the brain was injured and that it's picking up every time the brain's injured, but we're just not calling it an injury.

Jon Becker: Yeah. So, it's not as simple as you're going to go to a doctor and he's going to go, "Oh, well, that low-level blast caused a concussion." And it's just even in talking to the researchers that are doing some of because I talked to some of the researchers that are doing some of the biomarker data, and it's like there's no way for us to know for sure it's almost like we we know smoking is not good for you. We know it's damaging your lungs, but there's no test that's going to tell us that it's damaging your lungs until you have cancer and then we're going to go yep, you have cancer. It damages your lungs. That feels like kind of a dangerous game to play.

Dr. Daniel Daneshvar: That's exactly right. A lot of the biomarkers are probably related to injuries and injuries are related to the problems later in life, but the biomarkers might not be telling us anything about the problems later in life.

Jon Becker: So, we have to take any symptomatology very seriously then.

Dr. Daniel Daneshvar: Yeah, we absolutely need to better understand these symptoms and then track and make sure that we're minimizing the problems later in life by controlling the symptoms early on.

Jon Becker: Yeah. Because every time you have breacher syndrome or a headache or you didn't sleep well, that is your brain crying for help.

Dr. Daniel Daneshvar: That's exactly right. Our brain doesn't have any way to tell us that it's injured besides those ways.

Jon Becker: What are some other symptoms that I need to be paying attention to?

Dr. Daniel Daneshvar: Yeah. So, one other thing that can decrease your brain's resilience, your brain's ability to compensate for some injury is pain. So, if you think about my NFL players, right, they have been asked to hit people at really high speeds for a long time and that causes breakdown in their joints and their back. Think about the operators or tactical personnel carrying hundreds of pounds on their back and being asked to do all kinds of crazy things for years causing degeneration of their neck of their their lumbar spine of their joints. Those pain points can cause increased inflammation that travels throughout the entire body and that also increases inflammation in the brain. And so that can increase your risk of having degenerative problems later in life as well based on animal models.

Jon Becker: So you've got to take pain seriously.

Dr. Daniel Daneshvar: So you have to take pain seriously too. Even if it's not pain to your brain, pain in your body is something that I can treat that can improve your mental health and your cognitive health and your neurologic health.

Jon Becker: As Dr. Daneshvar told us, 90% of a SWAT team's blast exposure happens in training. That means we have real control over most of this risk. So, let's talk about what we can do with it. Earlier, I described how I've been thinking about this using the smoking analogy. Don't smoke more than you have to. Smoke the most filtered cigarette you can. And don't chain smoke. James Engel is a neuroscientist who has spent his career figuring out what each of those things actually means in practice for a tactical team.

James Engel: My name is Dr. James Engel. I'm a neuroscientist and co-founder of Blast Analytics and Mitigation. I study the effects of blast overpressure on the brain. So what we think is happening to the brain during repetitive low-level blast exposure is very different to what happens to the brain that is exposed to a large blast such as something from a high explosive like an IED.

When we think about overpressure and its effects on the brain, there's microscopic and macroscopic changes that are occurring following injury depending on the amount and of the exposure and the repetitiveness of that exposure. So low-level blast exposure spans from anything from 0.5 PSI and above. And then you can also think about the acoustics below 0.5 PSI. Things that you would measure in the dB range. So impulse noise for example is 140 dB which is still considered very loud. So to put things into perspective like a siren most people don't know that a siren's about 120 dB. Firearms depending on the type of weapon that you're using when we think about it and on the dB scale they occur anywhere between 160 to 171 dB.

So for this community, when we think of low-level overpressure exposure, your primary offenders are small arms. So handguns, rifles, large-caliber rifles, .338 and above. In addition to that, you have your energetics, flashbangs, explosive breaching. These are going to be the big offenders. If your team's going to be doing explosive breaching on a day, it's to train smarter. look at your training schedule and make sure that they're not doing combatives the day before, the day after to allow the brain to rest following a big training event.

So, the way that I frame this left to right of blast exposure type of solutions. So, when we think of left of blast exposure, we think of education, training and awareness and utilization of training tools. So, one of the things that we do at blast analytics and mitigation is that we teach and do a bunch of education on blast overpressure exposure, what it does to the brain, how to mitigate it, and you know, really to try to make the operator smarter in these scenarios.

So, In addition to left of exposure, you have time of exposure or during things that you could do in the moment. So, for instance, if you're going to be doing a lot of heavy weapon work or explosive breaching, large-caliber weapons followed up with CQB-type of training scenarios, these are the best times to throw on a suppressor to help reduce the amount of exposure that someone's getting at that moment. to the right of exposure.

Now, this is an interesting component because this is after the fact. It's really important for tactical medics on a team to be aware of the signs and symptoms of a concussion. And I know that in the literature they're talking about non-concussive injury. I still think of it as subconcussive forces because there are subclinical symptoms that arise that look like a concussion. And if there's ever any doubt in your mind, especially as an operator a tactical medic, the best thing to do is to refer them to their physician immediately.

There's a lot of parallels between low-level overpressure exposure and impact injury caused from different types of impact sports like soccer, football, MMA, and boxing. When it comes to low-level overpressure, you can think of it as these non-concussive forces, this invisible force that's hitting your body, right? And that overpressure, that pressure wave, it interacts with your body. Blast injury is very complex in several different ways and can have direct effects to the brain. So that shock wave, that blast wave is going to hit the person in their head, travel through their skull and cause injury to the brain. There's also indirect mechanisms where the blast wave shock wave hits the body, the torso, and then travels up through their vascular system into the brain.

So not only do they have to worry about direct and indirect effects but then there are other problems that if someone gets hit with a large enough explosion they can be knocked to the ground and also hit their head that way. So you can have compound problems in addition to getting the invisible wound but also impact injury as well.

One thing that you can easily do, every department can do this, and that is look at your weapon system, look at the device, understand what type of pressures are coming off of that system, and then make subtle behavioral changes or postural changes in the way that you may train and use that weapon system to reduce your exposure. For instance, a recent DoD study showed that if you make subtle postural body position changes, you can reduce your exposure to that blast by about 35%. Which is kind of fascinating because when you think about someone who's shooting a 50-cal most people think of someone shooting a 50-cal in the prone position. Well, most in this community, you're going to be shooting probably from a sitting position up in a crow's nest or bird's nest. One of the things that you want to think about is your surroundings. So, enclosed space will increase the duration of your exposure. It's important to train in those scenarios, but if you can train in a scenario where you can train in the open rather than a confined space, that is also another strategy. The harder the surface, the bigger the reflection.

So one thing about overpressure is that reflections can cause a Mach stem triple point in space. So you can literally get two to nine times greater the exposure based on where these waves are combining in space. So understanding where the Mach stem or Triple Point is also a critical tool so that you're not in it. As the explosive device is going off, there's a lot of energy that's being released. If you were to say throw a bang on the ground, the energy that's being released starts to reflect off of the surface and depending if it's concrete or if it's grass, the amount of that reflection is going to either double or quadruple the amount of energy because it's adding together as it's moving through space.

A lot of times people ask me like, "What's the difference between acoustics and overpressure?" Well, anyone who has ever been in a club and can experience null spots in space while they're in that club to that really loud bass, overpressure is insidious. It doesn't work that way. In fact instead of getting destructive interference, where you have two waveforms that interact with each other with sound and cancel each other out when two overpressure waves either from the initial blast or from the reflection when they combine with each other you get an additive or multiplicative effect. So you can get again anywhere between two to nine times greater energy in that point in space where they're combining. So when you think about it, depending on where you throw the device in that room, the energy is going to start bouncing off the walls and there are points there that are what we call “The Death Funnel” like in the corner of a room where energy is kind of combining. You don't want to be standing in that corner when that device goes off.

So knowing that reflective surfaces can increase your exposure when you're throwing a device or even if you're doing explosive breach making sure that you're aware of your environment that if there are reflective surfaces to maybe change your position or set up that position in the first place where you are maybe wrapped around a corner without any reflections that can potentially bounce the energy back at you. You can go from 4 PSI to 3 PSI with about one big step backward, about 3.5 feet.

We can take the literature and the approaches to for hearing conservation programs. Hearing conservation programs have been developed to help you maintain your ability to hear over time. There are specific protocols that are in place to limit the number of exposures per day per weapon system. The acronym for it is called ANOR (allowable number of rounds) per day that you can be exposed to. So that's frequency. And that will change based on your shooting position. So if you're standing, if you're kneeling or you're shooting prone, the closer the weapon system gets to the ground, the fewer number of rounds that you're going to be able to shoot. Understanding what the ANOR is for each weapon system is another useful tool to reduce exposures to that weapon system and stay below that number.

So the best way to understand what your exposure is is to do blast surveillance. When it comes to blast surveillance, it's just a matter of wearing simple gauges and those wearable blast gauges will give you a lot of information on the amount of exposure, the frequency of exposure, what type of exposure it is. You can leverage that knowledge to take an evidence-based approach to train smarter. So, know what your big training days are and make modifications as a result of that data. So, beforehand, you thought, well, everyone's past MSD. They shouldn't be getting four PSI or 3 PSI, and lo and behold, you look at your data and you are getting 3 or four PSI. This information can be used to make justifications to make training changes within your schedule.

So importantly, you know that you have a heavy day, maybe follow that up with a light day or you give your brain some time to rest. Don't do combatives before that heavy day and don't do combatives after that heavy day.

Jon Becker: Don't chain smoke. Give yourself time between cigarettes. In other words, give yourself time between blast exposures. Gary Kamimori's research turned up something that most teams have never thought about, what your helmet is doing to the blast wave.

Gary Kamimori: So, we've actually done a couple of different studies on overpressure inside the helmet. And the term that's used is “underwash”. So, it's the pressure going under the lip of the helmet and going up into the crown of the helmet. And because that pressure is coming in from all directions, when it meets at the crown of the helmet, those pressure waves are colliding. And when they collide, they combine. And that means the pressure is going to be even worse than what it was going in. So it's going in at 4 PSI. It's colliding at the crown of the helmet, and it's becoming 9 PSI. If you use an adjustable head suspension system, which leaves a gap between your head and the helmet edge, that's bad because all the pressure can go right up into the helmet. If you wear pads on your helmet that enclose your head within the helmet, it's hotter, but there's no gaps for the pressure to get in underneath your helmet and hence much safer. So pads are better than suspension. If you wear goggles, the top of the goggles and the bottom of the helmet meet, you've now decreased openings for pressure. If you wear eye protection, there's still a gap between your forehead and the helmet.

Jon Becker: The Marine Corps now prohibits instructors on catwalks from wearing helmets during breaching observations. That policy came directly from this research.

Gary Kamimori: For the underwash, we actually did some work for the Marine Corps because instructors in the catwalk were complaining that they were actually getting hit harder by the breachers that they were watching below them. And that made total sense because the pressure is coming from underneath them and directly up under the lip of their helmet. They are no longer required to wear helmets on the catwalk if there is no fragmentation issue. If there's a fragmentation issue, they wear a bump helmet.

Jon Becker: On suppressors, Kamimori’s team actually ran the numbers.

Gary Kamimori: We've done a fair amount of work, have a couple published papers on the use of suppressors. And again, something that we found is that the overpressure from the 50-caliber and 308 sniper rifles is below 2 PSI. It's not that significant. However, the acoustic exposure is huge. So, we've done comparative studies with and without suppressors, and we found that we can lower the acoustic exposure of the operator by 25 to 30% or more with the 50-caliber Barrett just by using a suppressor. But even with the M4, we found we could lower the overpressure to almost zero and the acoustics by over 50%.

Jon Becker: I started this conversation by comparing where we are right now to the 1950s and cigarettes. Scientists had the correlation. They didn't have the final proof. And the response for 1five years was essentially to wait. I don't think waiting is the right answer here. The researchers I've spent the last five years talking to don't think so either. The people who have already paid the price, Eric, Frank, Ryan, they make a pretty compelling argument for acting right now. When I try to think through how to communicate this problem to a team, I keep coming back to the smoking analogy because it's practical and it's honest. You may have to smoke, but there's no safe level of exposure here. Some of this exposure is unavoidable and the tools that produce it are essential. Nobody is arguing we should stop using them, but you don't have to smoke more than your job requires.

So, here's how I've been thinking about the solution, three things:

1. First, reduce how often you take the exposure. There are three specific ways to do this that we laid out in our article in the NTOA. Establish rules about exposure limits. The DoD implemented interim guidance in 2022 that set minimum standoff distances and daily exposure limits for weapon systems that produce blast overpressure. Those DoD guidelines are a reasonable starting point for your team. Look at them and ask whether the current training practices even meet that standard. 2. Second, rotate your cadre constantly. This is probably the most overlooked problem in tactical training. your instructors, your range safety officers, the people who are present for every evolution, they're absorbing five to 10 times the exposure of the operators that they are teaching and working with. One study found that up to 32% of blasts experienced by breaching instructors exceeded the recommended exposure limit. Watching a squad train from a catwalk or acting as the op four for training units can double or triple your exposure. Rotate your cadre. Track their cumulative numbers. Protect the people who are doing the most teaching. 3. Third, switch to training flashbangs. Live flashbangs run around 175 dB and produce a 1.6 PSI overpressure. Training flashbangs are 147 dB and drop that overpressure down to 0.065 PSI. That's not a small difference. If your team is running repeated CQB or HRT iterations with live flashbangs when training devices would accomplish the same training objective, stop. That is a cigarette that you do not have to smoke. 4. Next, mitigate the damage when you do need to take an exposure. Smoke the most filtered cigarettes you can find. Here's what that looks like in practice: Run suppressors whenever possible. Kamimori and his colleagues published research in the Tactical Edge showing that suppressors on a 50-caliber rifle provided a 92% reduction in pressure readings compared to no muzzle device. 92%. That was for a 50-cal. The effect carries across other weapon systems. Suppressors also reduce reflected wave exposure for everyone else in the area. If your team has suppressors and is not using them in training, this is a straightforward decision to revisit. 5. Next, think seriously about your range environment. Concrete walls, metal roofs, narrow hallways reflect blast waves back onto the people training in them. The Marine Corps noted that positions closer to the ground experience higher blast overpressure due to surface reflection, which is why shooting prone puts you at greater risk than standing. Small changes matter here. Rubber floor mats, spacing shooters out, shooting over grass rather than over concrete, acoustic foam on metal ceilings. These all are not complicated or expensive changes, but they're filtering the cigarette. 6. Next, establish a training safe distance separate from your operational minimum safe distance. Your MSD is designed to balance exposure risk against entry timing in a real operation. Your TSD in training should be doing something different. It should be trying to get exposure as close to zero as possible. In practice, that may mean extending your MSD by a few feet, or it may mean putting a 90 degree corner between the team and the charge during training evolutions where nobody is practicing immediate entry. Because of the exponential relationship between distance and blast pressure, small increases in standoff distance produce large reductions in blast exposure. 7. Finally, recover before you take more exposure. Several of the experts we spoke to described the effect of re-exposing an injured brain like scraping a scab off during a healing cut. You prevent the body from doing its natural repair work. Do that often enough and the body stops trying to heal and just builds scar tissue instead in the brain. The practical application is about your training calendar. If your team is planning a week of training, put the explosive breaching refresher and your HRT or CQC iterations at opposite ends of the week, not back-to-back. Within a monthly schedule, try to allow weeks between those heavy events. If you're running an 8-hour flashbang training, consider splitting it into two 4-hour blocks on separate days. Simply put, breaching training and HRT training on the same day or on consecutive days is probably not the best decision if you have the flexibility in the schedule. One of the experts I spoke to recommended allowing at least 72 hours between significant exposures, and that includes combatives and contact sports because any impact in the head during recovery from blast exposure is reopening a wound that is not yet healed. Pay attention to symptoms. I want to be honest with you about something here. In a community where pain is a constant companion, where durability is a professional requirement, and we're admitting something wrong has historically carried a real cost, saying “listen to your body” is not enough. So, let me be more specific. Headaches after training, difficulty focusing, brain fog, difficulty sleeping the night after an exposure, irritability, poor impulse control. These are not signs of weakness. These are the brain's only available mechanism to tell you it has been injured. It does not have pain nerve endings the way that your ankle does. Symptoms are the signal. And the best way for this to actually change is for leadership to build a team culture where those signals are treated with the same seriousness as a broken ankle. A teammate with breacher's brain symptoms needs to recover before the next exposure. Exactly the same way a teammate with a sprained ankle needs to stay off it before the next run.

Eric Patrick's told me that if his team had known what we know now, he doesn't think he would have been talking to me. Frank Larkin's son, Ryan, told his father for years that something was wrong and nobody listened. He was right. He donated his brain to science to prove it. We know now. That puts it on us.

One more thought before I hand it off. The Department of Defense has launched genuinely massive research programs on this problem. Special Operations Command has made this a stated leadership priority. The Blast Overpressure Safety Act is now law, passed in December of 2024. Baseline brain scans are going into military medical records. Researchers are working on blood-based biomarkers, better imaging, blast exposure tracking systems. That work is critically important and I don't want to understate it but it will take time-- years certainly possibly longer before we have the complete scientific picture. The definitive proof of mechanism, the established safe thresholds and the validated clinical interventions are years away. That is the nature of this kind of research. It is hard and it is slow and it will not be finished before your people absorb the next round of exposures. Which brings me back to where I started. Correlation always precedes causation. The direction of the evidence is clear. The DoD did not wait for proof before acting. They established interim thresholds, mandated tracking, and started scanning recruits. That is the right call and it's exactly what I'm asking you to do on your own team. Don't wait for certainty. Act on what we know now and update as the science develops.

Before we go, I want to take a moment to thank the people who made this episode possible. Dr. Gary Kamimori, Dr. James Engel, Dr. Daniel Daneshvar, Eric Patrick, and Frank Larkin. Special thanks also to Josh Watford from CATO. Josh's literature review formed the scientific backbone of both the NTOA columns that we wrote and this podcast.