So, you're a journalist, or maybe an activist, and you're looking for information about protecting yourself from what are euphemistically called "riot control agents". By now, you've probably discovered that information on the internet about this topic is either outdated, inaccurate, or not necessarily applicable to your needs. As a photographer with some experience shooting with both full- and half-face respirators and gas masks, I've put this page together to help you make an informed decision about protecting yourself.
Important disclaimer: I am neither a lawyer, nor a trained chemical- or biological-warfare defense specialist. The information on this page is purely "as is", with no warranty expressed or implied, et cetera, et cetera. In particular, this page is concerned with defending against three principal irritants - oleoresin capsicum "pepper spray", and CN/CS "tear gas" - used in domestic law enforcement environments. The advice here does not necessarily apply to other chemical and biological threats from military or terrorist action.
As you probably know, information on the web about choosing gas masks and respirators comes from two main sources: paranoid paramilitary guys who want to defend against every chemical, biological, and radiological threat known to man, and activist groups whose recommendations, not surprisingly, often conflict directly with those of the gun-toting militia members. For the narrow area of protecting against riot-control agents at a demonstration or rally, either as a participant or journalist, both groups' advice is, frankly, lacking; the recommendations of the gun nuts are usually overkill, and much of the activist advice is, well, just plain bad.
OC, CS, and CN - the three chemicals of choice for law-enforcement use - are very different chemically, but affect people in similar ways. All three are severe eye irritants, and unpleasant - to say the least - when inhaled, either orally or nasally. You will cry, snot will run out your nose in an unstoppable river of goo, and you will be downright miserable if exposed to any meaningful amount of these compounds. Been there, done that, it's not that fun. Neither CS nor CN "tear gas" are actually gases; they're very fine particles. Pepper spray is usually an aerosolized liquid, but the fumes are also irritants. So, what you want is eye and respiratory protection against particulates and "organic vapors", and there are two basic ways to achieve this: A full-face respirator or gas mask, and a half-face respirator paired with goggles.
There are a lot of military-surplus gas masks out there. My recommendation is to avoid them all. You'll either pay too much, get a non-functioning antique, be unable to find current, "fresh" filters, or be unable to easily get replacement parts. Or more than one of the above. Don't get caught up in debates about which masks resist nerve agents, and which masks are easiest to change filters on; avoid them all for use at or around domestic disturbances.
A better option is a commercial full-face respirator, which is basically a non-military gas mask. Most of the time, you should be able to get a brand-new (not "refurbished", or "like new", or "new, old stock") full respirator from a company like SEA, MSA, 3M, Draeger, or Avon for well under $100. There are a huge number of models with a bewildering array of features, but for the purposes of this page, I'm going to say there are three things you need to consider:
First, make sure you're looking at a respirator, and not a forced-air (or on-demand) "facepiece", meant to be used with an air source like a SCBA. You want something designed to use with filters or "cartridges", depending on the manufacturer. Second, figure out what kind of filters it takes, and how many (either one or two). They'll either be "NATO standard" 40mm screw-fit filters, or some kind of proprietary or semi-proprietary filter. My advice is to go with a respirator that takes 40mm filters, because it's easier to find ones that will both fit, and be designed to protect against riot-control agents.
The third thing to consider is the facepiece, or visor - whether the respirator has a one-piece visor, or a separate "window" for each eye. The trend is towards masks with one-piece visors, allowing a wide field of view, but most of these are terrible for trying to use a camera with, because the glass, polycarbonate, or whatever is so far from your eyes. Respirators with individual eyepieces are much easier to use a camera with, in my experience. Among the single-piece masks, some are "hard", but some are actually made of flexible, transparent rubber. I've yet to try one of the flexible-lens masks, but I have my doubts about how well they would work with a camera - or how much physical protection they provide. Obviously, if you're "chimping" with your digital camera's LCD screen, this is less important - and with an optional polycarbonate lens cover, available for most such masks, irrelevant.
One noteworthy exception is MSA's "Phalanx" mask, a full-face gasmask designed purely for law-enforcement use. It's described as "low profile", and was designed to be worn under a riot helmet with visor. As such, while the lens is a single large piece, the whole thing is almost as close to the eyes as those on more conventional, two-lens designs, while offering better visibility.
The other big advantage of the two-lens masks is that they generally fit into a smaller space than the single-big-lens kinds. Some masks take up twice the space of a shoebox; others fit into considerably less space. Remember, "tactical carry" was not a design criteria for most non-military, and even some law enforcement respirators...
The price of surplus military gas masks rose rapidly after 9/11/01, and isn't likely to drop any time soon; it's simple supply and demand, really. However, the market is absolutely saturated with brand-new masks and full respirators intended for law-enforcement and "first responder" use, many of which have become - incorrectly - viewed as "obsolete". In my opinion, these represent the absolute best value out there in a mask today, because the paramilitary nuts won't touch them with a ten-foot pole, thereby keeping the market prices ridiculously cheap.
Here's what happened: Before 9/11, a number of manufacturers marketed full-face respirators to law enforcement for protection against "riot control agents", dust and particulate hazards, and sometimes a small assortment of industrial hazards. After 9/11, everyone became paranoid about nerve agents, biological warfare agents, and other military nasties that, so it's theorized, law enforcement will have to deal with as a result of terrorism, and it turns out that a lot of the masks marketed to law enforcement either weren't rated or certified to withstand certain chemical weapons - mustard gas being perhaps the most common - or the filters wouldn't protect against some industrial chemicals theoretically usable by terrorists, like chlorine gas. By late 2004, a couple new military-style masks had arrived on the market that met the government's newly-revised NBC-terrorism guidelines, and the previous masks became, to a lot of people with more paranoia than common sense, worthless overnight. So it is that you can get fresh, recent-vintage $150-$300 masks for $20 to $40, new, as they're being dumped on the market by manufacturers and distributors who got caught flat-footed by the sudden shift in demand. All these recent masks have filters available - or take standard 40mm cartridges - and should remain so for the forseeable future, thanks to continuing demand from a lot of public safety agencies who bought all new masks right after 9/11, and can't afford to "upgrade" again anytime soon.
Whatever mask or respirator you go with, be aware of its limitations. You need a certain minimum amount of oxygen in the air you breathe to live, and a respirator does not provide this. If the only thing you have is a mask that doesn't seal perfectly, and a questionable, outdated filter, it's probably good enough to let you immediately leave the area when riot-control agents are used. Even having a properly-fitting mask and a new, chemical-warfare filter doesn't mean you necessarily should hang around once things start getting ugly - nor do they confer upon you the ability to pick up a burning tear-gas grenade without being burned, or grapple mano a mano with well-armed and -armored law-enforcement officers. Polycarbonate or laminated safety-glass lenses are not bulletproof, and aren't designed to stop rubber bullets or other sorts of projectiles. Yeah, you can dress all in black, and wear a gas mask that looks badass, but that doesn't make you badass.
If you really want to go with a half-face respirator, the major consideration is what kind of filters the mask takes - 40mm or proprietary. Again, 40mm masks are a better choice, in my opinion, but a lot less common. The big problem becomes finding goggles that will actually provide an air-tight seal. As far as I can tell, the options are to get relatively tight-fitting "ballistic" goggles and seal them yourself - silocone caulk being a good choice - or hunt up some "sealed" goggles meant for laboratory use. The former probably provide better protection, once sealed - but the latter are usually designed to fit well with a respirator. While you might be able to save a few bucks by using a half-face respirator and goggles, it's really just easier to get a full-face mask, in my opinion. Another consideration is that not as many half-face respirators seem to include speech emitters as do full-face masks; this could be important to you, should you need to say something like "don't hit me, Officer, I'm a journalist"; "mmpf mm muh, mmpfer, um muh mmpf pfffh" just doesn't have the same ring to it.
Too, by their very design, half-face masks fit a much smaller number of people correctly, because they're less tolerant of differing facial features. In particular, those with prominent chins or noses, or even moderately large heads or faces, may be unable to find any half-mask that fits properly, even those in "large" sizes.
As far as filters go, much depends on whether your mask accepts standard, 40mm screw filters or something else. If your respirator uses 40mm filters, the absolute best option, in my opinion, is Scott's "enforcement cartridge", which has a ten-year shelf life, costs a mere $20 at places like Botach, and is specifically designed to protect against CN and CS, as well as a whole host of other unpleasant things. If you can get an unexpired, unopened military C2 or C2A1 filter, or similar NBC filter, for less, by all means go for it - but for peace of mind at a civil disturbance, a fresh $20 cartridge designed to protect against riot-control agents is hard to beat. If your mask does not take these standard filters, you want the "best" filter the manufacturers offer - this will typically be a combination filter, providing both P100 particulate protection and protection against a very wide range of chemicals and "organic vapors". If you've got an MSA or AO Safety mask, for example, that take the two little screw-in cartridges, go for something like MSA's "GME-P100" filter. This is, strictly speaking, overkill, as a "P100" filter (99.97% efficiency against particulates) rating is the standard for protection against CN and CS, but the additional protection costs little extra and provides additional peace of mind.
There's a lot of debate about filters "expiring". Some manufacturers' filters "expire" after two, three, or four years; others "expire" after eight, ten, or even twelve years. Some - like AO Safety's - never expire at all. All go "bad" sooner or later once opened, of course - primarily due to moisture - but a lot of people allege that "expiration dates" on filters are just a scam by the manufacturers to keep up a steady stream of revenue. Even those who believe in the validity of filter expiration agree that "old" filters should still protect against particulates, like CN and CS, and there are many activists who've used 1960s-vintage (and even older) filters effectively at WTO demonstrations and the like. Nonetheless, I suggest buying new, fresh filters; they often cost no more than surplus filters, and you know they're good. If you're going to buy old, surplus filters for use against riot-control agents only, try to get the newest filters you can; older ones may themselves contain nasties like asbestos, and often offer more breathing resistance than newer designs. At the very least, make sure you know what you're buying; a lot of unscrupulous sellers are misrepresenting older filters as offering "full" protection against NBC threats, and charging accordingly; don't, for example, get suckered into paying $40 for a "new" 1970's-vintage German or Israeli tear-gas filter described as a "NATO NBC filter", which sell at honest merchants for $5-$10. Oh, the tear-gas filter will probably still work against tear gases; but why pay four times the actual market value? A new mask should come with a filter or filters; you might want to keep this for "real" use, and use a cheap, surplus filter to confirm mask functionality, but otherwise new ones are the way to go.
One other thing to consider is the comparative size and ease of carrying of spare filters; most non-standard filters are the size of a hockey puck, or smaller, but the 40mm filters are a bit larger than a softball. Two smaller cartridges the size of shoe-polish cans might be easier to carry in a camera bag or cargo pants than a single, 40mm filter. If you're already wearing a camera bag, and a bag for your mask, carrying another bag to carry filters in might be awkward, to say the least.
Whether you actually need extra filters is a matter of some debate. Most cartridges designed for use against CN and CS are certified to provide protection for "at least eight hours" of exposure (i.e. more than 480 minutes) at a certain level of concentration, and should provide a similar level of protection against OC as well. That said, it's better to be safe than sorry, and some things - notably, exposure to water or other liquids - can render a cartridge ineffective prematurely. There's probably no need to carry a bunch of filters, but an extra - or an extra set, if applicable - is probably wise, just in case. One option you may wish to examine is that of filters, or "prefilters", which are available to mount over other mask or respirator cartridges. Usually thin discs of paper filter media that are held in place with plastic or metal retainers, these filters generally offer P100 particulate protection, and their use could considerably prolong the useful life of a mask cartridge exposed to particulates; when breathing becomes labored, pop the filter off the cartridge, and either replace it, or go without.
Many respirators that take 40mm filters have the filter mounted on the front; this can be awkward at first, and depending on the camera you use and what eye is your strongest, may or may not interfere with photography. If you're "right eyed" you'll probably have less problems than those of use who are "left eyed", because of where the viewfinders on cameras tend to be. For those that take a 40mm filter on the side, you can usually switch which side the filter is on, and make it easier to use a camera. Those which take two proprietary filters usually need to be used with both filters fitted.
As far as cameras go, anything with a tiny, squinty viewfinder just isn't going to work with a mask, because you won't be able to get it near enough to your eye to see anything. Because of limited head movement when wearing many respirators, a TLR isn't going to work, either. If you don't want to chimp the LCD on a digital camera, your best bet is to find the camera with the largest viewfinder you can find. If that means going back thirty-five years and using a "sports finder", so be it; whatever works should be the mantra. (Some sports finders are much "squintier" than others, alas.) The problem with little viewfinders is that, from a short distance back, you can't see the corners; from a little further back, you can't even see the sides of the frame, and might as well just point and pray. If you have an autofocus camera with a prime lens, consider some of the auxiliary shoe-mount viewfinders made by Voigtlander for their line of Bessa rangefinders; some of them are huge and bright, and should work acceptable with a respirator. Whatever you use, you might want to get a rubber eyecup for the body, both to keep the camera from scratching your mask, and to keep it from sliding all over; this is a much bigger problem with newer masks with one-piece faceplates than the old ones, whose eyepieces usually have a ring of nice non-slip rubber around them. Whatever the camera, verticals can be a challenge to shoot, because the camera doesn't fit against the mask quite how you'd like in that orientation. If you've got a mask with a single, side-mounted filter, take special care about keeping your horizons level. I know, I know, Photography 101 stuff, but the lopsided weight of the filter and mask may mean you're walking around with your head unconsciously cocked to one side.
Though it seems obvious, remember that any of the eye and respiratory irritants you happen to be exposed to might well be on your skin, your clothing and equipment, and the outside of your respirator. Removing your mask once in a clear area, and promptly wiping your eyes or your nose with a hand contaminated with riot-control agents is a rookie mistake you really don't want to make.