There is a myth that if you can talk you must be able to breathe, and in light of recent events in America it is really important that we look at this.
The first important fact to grasp – the lungs have “Volumes” and “Capacities“. For our purposes, you need to understand 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).
https://www.bbc.co.uk/bitesize/guides/z3xq6fr/revision/2 is a good guide to how the lungs work. Average capacity (premium) is 6 litres. When you take a breath under resting conditions, you are breathing in about 500ml of air (varies obviously on age, size, weight, medical conditions, etc). Under exertion, this can increase six-fold. After breathing out, you are left with ~2400ml of air, this is 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. 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.
The lungs work on negative pressure. Your lungs, when you breathe in, are at a lower pressure than the outside air. This draws air into them. Your lungs are elastic and will move back to their normal size during exhalation. This is where the problem begins. If you are restricting that inflation, there is a strong possibility that you can cut off the ability to breathe. Once the lungs begin to exhale, they collapse, but if they are being restricted, 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. They are now in deficit. So, although someone is telling you they can’t breathe, they may not be capable of re-inflating their lungs. During physical activity, this likelihood is increased – and incidents of control and restraint will quite happily sit under a description of increased physical activity.
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 words (and my lungs are medically shot!), 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. This is where the Functional Reserve is being used. There is no air coming in, just going out.
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.
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.
Positional/Arrest Asphyxiation is taught on all courses where there is a need to actively restrain, control or detain someone. A detained person does not need to be laying down for this to come into effect.
This is not to judge or pass comment on any cases or incidents – it’s a guide that should prod your memory at the right time. Only you can justify why you took a course of action – but you may have to explain why you took that course of action, based on the knowledge you have and the training you have undertaken.
If someone is saying they can’t breathe, you need to explain why you chose one force option over another and justify that decision in line with the law and your training. It’s not an easy subject, and in the heat of the moment it may not be at the front of your mind, but at some point you need to consider the issues that face you – or a colleague.
Remember – A person saying they can’t breathe doesn’t mean they can breathe because they are talking. It could be the last words they are able to say.
Adam has had a long and varied career, working within physical and communication intervention fields, ranging from military to education, mental health and secure units and is now the Personal Safety Training Manager for Hampshire Constabulary.