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Tuesday, January 04, 2011

Physicians for Human Rights can't figure how tear gas could kill people outdoors

Physicians for Human Rights wrote a paper in 1989 to try to make tear gas sound as dangerous as possible. Here's the main point of the paper concerning CS, which is the type used by the IDF and Israeli police.

After discussing how CS could be potentially lethal if used indoors, the paper says:

The respiratory concentration of CS that would be lethal for 50% of healthy adults has been  estimated to be 25,000 to 150,000 mg/m 3 per minute, based on animal studies (15). When  detonated outside, a CS grenade generates a cloud 6 to 9 m in diameter, at the center of which a  concentration of 2,000 to 5,000 mg/m 3 can be produced, with concentrations rapidly tapering off  at the periphery. (16)

So for it to be lethal for a normal adult, there would have to be exposure for a full minute at concentrations that are ten to thirty times higher than is physically possible outdoors. I don't know how long CS takes to disperse, but certainly the highest concentrations of up to 5000 mg/m3 would not last for more than a few seconds.

The studies done of people who have been seriously injured from CS all show that they were indoors at the time, and had prolonged exposure - far more than a few seconds - and they could not leave the room.

I cannot find any case of someone succumbing quickly (within a day) to any level of exposure to CS.

In 1989, some human rights groups charged that Israeli use of tear gas - the more dangerous CN gas at the time - was responsible for increases in miscarriages and even 400 deaths. A US government GAO study found the claims to be baseless.

So this is nothing new.

UPDATE: Some blogs are saying "The U.S. Army Center for Health Promotion and Preventive Medicine warns that at a concentration of 2mg per cubic meter, CS gas “is immediately dangerous to life…”

The document does say that - and it is a typo.

The document cached here says that for CS,

LCt50 = 61,000 mg-min/m3

which means that the median lethal dose of CS is 61,000 mg per cubic meter for a full minute - well within the range described by PHR and way, way higher than is possible outdoors. There is simply no way that it is dangerous to life at 1/30,500 of the median lethal dose, if the words "median lethal dose" have any meaning.

Not to mention that if the dose of 2 mg/m3 is immediately dangerous to life, then Bil'in protesters would all have been dead for years. A minor point.