From: John De Armond
Subject: Re: Gas Masks
Organization: Rapid Deployment Systems (making go-fast things and things that-go fast)

ren@virga.rap.ucar.EDU (Ren Tescher) writes:

#On the first day of NBC training at Fort Leonard Wood (pronounced
#Four Letter Word ;^) )  we were told that chlorine and ammonia
#molecules were too small to be trapped by the activated charcoal filters
#in the M17 gas masks.  What you might consider is a Self Contained
#Breathing Apparatus (SCBA) such as those sold by oil field safety
#companies which have a 5-minute or so air-supply to enable the
#'worms' to get upwind of an H2S leak (hydrogen-sulfide=bad stuff).

THere are chemical cartridges that are effective against ammonia, at least,
and I suspect chlorine too.  I used to have to wear such a beast when 
I was the operator of an Ammonia cooled ice plant that leaked about as
much ammonia as it used :-)  

The major problems with any of these devices is that their capacity for
absorption is fairly low and the protection factor is also somewhat low.
A PF of 100 is typical (that means that you can safely breath an
atmosphere 100 times the concentration considered safe with no protection.
Self-Contained Breathing Apparatus (the ubiquitous Scott Air Pack) typically
offers a PF of 10,000 or more.  Be prepared to pay >$1000 for a 30 min
SCBA.

A couple of other devices are available that give moderate PFs and long
duration.  One is known as a "rebreather" which contains a chemical
pack that reacts the carbon dioxide in the exhaled air and releases 
oxygen.  The user rebreaths most of his air in a closed loop.  The second
type is known (if my memory serves me) as the ChemOx pack.  It contains
a chemical that slowly burns and releases oxygen in the process.  This
chemical along with a filter pack is contained in a chest-pack.  You can
typically get >30 minutes of protection with this type unit.

If you want to find out the latest in toxic gas protection, drop into
misc.emerg-services which is where all the emergency services types hang
out.  Good current poop there.  My information is at least 5 years dated.

John