In the dojo, our safety training is almost always focused on safety in the dojo or our own artificial laboratory conditions. After all we want to train and play safely. Often though we fail to look at real life consequences or dangers that our techniques possess. After all if we are merely trying to protect ourselves using a throw and the person hits their head, our soft techniques become inadvertently lethal. This happened just a few months ago in my fair city. A young man died.
For those of us in grappling and restraint arts there is a danger I have never heard a single martial arts teacher lecture about. The danger is positional asphyxia. When we train and our partner can tap out when they are uncomfortable. However if you have ever restrained a strong, angry person you will know the problems continue throughout the restraint. What if they keep fighting? What if they remain angry and dangerous? What if you are morally/legally bound to cause no injury to the person?
Often a long restraint gets tighter and tighter. The person being restrained has a feeling of helplessness and will exert energy beyond their means to keep the fight up. There is always scratching and biting involved. Nothing is like in the dojo, the conflict does not end with a cheery tap. The conflict can go on and on. People DO DIE from the act of being restrained.
Positional asphyxia, is also known as postural asphyxia, is a form of asphyxia which occurs when someone's position prevents them from breathing adequately. A small but significant number of people die suddenly and without apparent reason during restraint by police, prison (corrections) officers and health care staff. Positional asphyxia may be a factor in some of these deaths.
* Positional asphyxia is a potential danger of some physical restraint techniques,
* People may die from positional asphyxia by simply getting themselves into a breathing-restricted position they cannot get out of, either through carelessness or as a consequence of another accident.
Research has suggested that restraining a person in a face down position is likely to cause greater restriction of breathing than restraining a person face up. Many law enforcement and health personnel are now taught to avoid restraining people face down or to do so only for a very short period of time. Risk factors which may increase the chance of death include obesity, prior cardiac or respiratory problems, and the use of illicit drugs such as cocaine. Almost all subjects who have died during restraint have engaged in extreme levels of physical resistance against the restraint for a prolonged period of time. Other issues in the way the subject is restrained can also increase the risk of death, for example kneeling or otherwise placing weight on the subject and particularly any type of restraint hold around the subject's neck. Research measuring the effect of restraint positions on lung function suggests that restraint which involves bending the restrained person or placing body weight on them, has more effect on their breathing than face down positioning alone 
There is a degree of controversy amongst researchers regarding the extent to which restraint positions restrict breathing. Some researchers report that when they conducted laboratory studies of the effects of restraint on breathing and oxygen levels, the effect was limited. Other researchers point out that deaths in real life situations occur after prolonged, violent resistance which has not been studied in laboratory simulations.
ASPHYXIATING” POSITIONS RANGE FROM
* a position that obstructs the mouth and nose (“upper airway”); or
* a position that causes hyperflexion (extreme bending-forward) of the neck,
so as to obstruct the trachea (the largest “lower airway” passage); or
* a position that causes restriction of the chest or diaphragm –
a position that impedes or prevents the MECHANICAL means of breathing;
* OR a combination of any of the above-described asphyxiating positions.
The above is a slice from the following excellent website. Look at this link and inform yourself about the realities of the consequences of your restraints
From Great website about positional asphyxia