Bump his tomorrow-I think I have the relevant info somewhere at work.
Basically, OSHA only regulates a couple of LE aspects, and they do not enforce either heavily. One is bloodborne pathogens; your agency has to provide safety training, gloves, masks, body suits and decon supplies, certain vaccinations, and minimum levels of treatment post-exposure (including expensive "Protease coctails").
The other one is HazMat. The requirement is that is your agency responds to any kind of HazMat incident, it has to provide masks, suits and training for first responders. The MSA masks work fine for this, and we just bought a bunch last year, pre 9-11 (someone was actually thinking ahead). M17s won't cut it, because they aren't rated for many industrial toxins, which is the reason LE is required to have this stuff. The nice side benefit (if you can call it that) is that a WMD incident is essentially a HazMat incident, so the same gear works for both.
These masks are far more useful for riot control, perimeter or dealing with someone who just got a liberal application of OC (you need a mask if you use pepperball on someone).