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.