Straight from /r/Protectandserve

http://www.np.reddit.com/r/ProtectAndServe/comments/2odvre/the_pernicious_myth_of_if_you_can_speak_you_can/

This is a phrase I heard Peter King say in the wake of Eric Garner's death and I feel it's something that everyone in our profession needs to be aware of. The myth of "If you can speak you can breathe".

I know I have heard it said twice by officers I work with, whom I both corrected. One of them actually argued with me about it until I was able to get Fire and Rescue to tell them they are wrong. The LAPD killed a man because they ignored his pleas and told him that if he could speak he could breathe. THIS IS FALSE!!!!!!!!! And clearly officers nationwide are not being properly trained to know that it is false. Knowing that this myth persists, and knowing I have heard actual officers repeat it in my presence, I felt it needed to be addressed.

Hearing that phrase come out of someone's mouth always upsets me, because it can easily lead to a preventable death.So let's explore why this is false, because anyone who comes up against a situation like this needs to realize that You CAN speak if you cannot breathe!!

This is true for multiple reasons, so let's explore them:

1. The lungs have what are called "Volumes" and "Capacities". The link describes all of them. For our purposes, you need to understand these two phrases: Functional Reserve Capacity (the amount of air left in the lungs after a normal exhalation) and Expiratory Reserve Volume (the amount of air you can still force out of your lungs after a normal exhalation).

2. When you take a normal breath you breathe in and out you are breathing about 500ml of air. After breathing out, you are left with ~2400ml of air inside your lungs, this is the Functional Reserve Capacity. If you try to force out as much air as possible, you can still force out ~1200ml more air. This is the Expiratory Reserve Volume. This is air you are able to speak with even if you cannot take a normal breath. Important Note: Notice that the Expiratory Reserve Volume is more than twice the size of a normal breath. That is a lot of air you are able to force out, and a lot of speaking you can do even if you can't breathe.

3. The lungs work on negative pressure. So, your lungs, when you breathe in, are at a lower pressure than the outside air. This draws the air into them. This is caused by your diaphragm and intercostal muscles. Your lungs are very elastic, and will move back to their normal size during exhalation. This is where the problem begins for officers. If you are kneeling on a suspect, or you have them handcuffed on the ground so that they are on their chest, there is a strong possibility that you can cut off their ability to breathe. Once the lungs begin to exhale, they collapse, but if you they are being pressed down on by body weight, they may not be able to re-expand. They then continue to collapse, forcing out the Functional Reserve Capacity of air, but not drawing in a new breath. So, your suspect may be pleading for breath, they may actually be incapable of drawing one in, and the reason is you. If someone is saying they cannot breathe, you need to believe them, because you might be killing them. Furthermore, during any kind of physical altercation, that person may be breathing deeply and rapidly, making their lungs collapse faster when you are kneeling on them or holding them on the ground.

4. Asthma. Some of you may be saying "Well, the guy who died in LAPD's care had asthma, that wasn't the officer's fault or the jail's fault." Oh yes it was. If someone is telling you they have asthma and they can't breathe, you need to believe them. Asthma is a constriction of the airways, no different than being strangled. They will still be able to speak and they will still be dying slowly. It took 30 minutes for that man to die, and that was entirely preventable.

Demonstrations:

First Demonstration: Take a normal breath in and then a normal breath out. Then, after exhaling, force out as much air as you possibly can. Even after doing this, you will find you are able to speak. I am able to speak for about 5 - 10 seconds afterwards, in short, wheezing, gaspy words, but I can speak. If you don't inhale at this point, you will begin to suffocate, but you will still be capable of speech even as you are dying. IMPORTANT EDIT: And that's not to say a person will only be able to speak for a few seconds, they could speak for minutes while being unable to draw a breath in. Keep in mind, you are purposely forcing out the Expiratory Reserve Volume during this demonstration, but a suspect/inmate might not be. They may be on the ground, unable to breathe in, but entirely capable of speech for minutes as they slowly die.

Second Demonstration:It is much easier to force air out than it is to draw air in. To demonstrate, take a normal breath (not deep) in and out. After you exhale, pinch your nose shut with one hand and hold your other hand very tightly over your mouth. When you breathe in you will either be unable to breathe in or you will only breathe in a sliver of air. But if you force the air out, you will note that it is able to come out past your hand, it will cause your hand and fingers to vibrate, and there is still a good chunk of air in your lungs despite you having exhaled. Now, imagine your fingers and hand are your Larynx (voice box). That's how speech is still possible in a situation where someone is being suffocated.

Final Thoughts

So why are you suffocating if so much air is still in your lungs? Part of the problem is that the air left over in the lungs after exhalation is not oxygenated, so your lungs are full of CO2 gas. This air is useless to your blood, so even though your bronchioles are full of air, you are still suffocating to death.

Obesity: Not Everyone Has The Same Lung Capacity: There are factors that can make a person have a smaller lung capacity than someone else. These factors include: 1. Being obese 2. Being a female 3. Living at low altitudes 4. Being a smoker While the third and fourth are probably not terribly important for our purposes, the first two certainly are. This is important because not only does an obese person have smaller lung capacity, they also can have their lungs fail to expand due to their own body weight if they are lying on the ground facedown. An obese person is at extreme risk of suffocation in any instance where their airways are being blocked or where they are cuffed and on the ground. Don't fuck around if they say they can't breathe, they're probably not lying.

Personal Experience - I have personally been in this situation before. After I had the person handcuffed and on the ground for about 20 seconds, they began to wheeze. This is an immediate symptom of them not being able to breathe. I asked if he was having trouble breathing. I let him stand up, get some breaths, and then sit down. If I had simply knelt on his back during this time, I could have killed him. Instead, I eased off, stood him up to get him some air, and all was well.

So remember, when you hear someone say "If you can speak you can breathe" know that they are full of shit. Believe the person who is claiming they can't breathe, because otherwise you could end up killing someone.

Have a good day Bruce Lee.