MSA Chemox


Home Main Database Database USAPage up Photos MSA Chemox
         MSA Chemox SCBA
Date: 20 June 2003
JW. Bech
MSA(Mine Safety Appliances & Co)
 Design 1947
Pittsburgh Pennsylvania
Land of origin
Special Note: 
KO2 chemical unit
User group
Minerescue, Military
Part no:
Working principle
Gas type
Cylinder volume
Max. cylinder pressure
Material of cylinder
Counterlung inspire
Counterlung exhale
Operational time
45 minutes
Operating temperature
Magnetic signature
Weight ready to use in Air
Weight ready to use in water
Scrubber material
Dual hose, with valve
If you have any information to add this sheet please mail it to References to source and names will always be added!  
Info found: If you like to receive a manual of the MSA Chemox rebreather, please sent me an email and I will mail it to you. The manual is property of the factory, so the copyright has to be respected. Only to be used for educational purposes!
 Also in our museum is a MSA Chemox or Navy Breather. The Chemox breathers were placed in service in Woodbury during February 1960, fifteen years after World War II ended. Chemox is a reference to the oxygen producing chemical in the canister. The Chemox units had a canister that generated oxygen from the moisture in the breath of the user. There were two exposed soft bags or lungs that stored the oxygen for the user. The lungs and canister were worn on the chest of the user. To start the unit you would insert the canister by screwing a clamp at the bottom which would force the top into a piercing device. This was known as lighting off the unit. You would have to inflate the lungs. This would "prime" the unit. The moisture in the storage lungs would start the chemical reaction. Then you would put the mask on. Once you started breathing into the mask, your breath was routed into the canister were the moisture would continue reacting with the chemicals releasing more oxygen and at the same time absorbing carbon dioxide.


The units had a manual timer that the user would have to set when he lit off his canister. The timers could be set to 60 minutes. However the canisters were only rated for 45 minutes. The canister generated a great deal of heat during the chemical reaction. The user was protected by an air space provided in the chest harness thus keeping the canister away from the body. Disposal of the canister today is considered hazardous waste. The Woodbury Fire Department stop using the Chemox breathers in the early 1970's. However the United States Navy is still using the Chemox breathers on board their ships today (as of the last time we checked  in 1998).
Information added by J. Lutz dd 27-12-2008:

Your article states the as of 1998 the MSA Chemox was still in use in the U.S. Navy, and while I'm not sure of what my American counterparts are using these days, the Canadian Navy is still using the Chemox as our main firefighting breathing device, the exceptions being rapid response and hazmat situations for which the MSA Stealth air bottles are used.  However, plans have been approved to replace both systems with Drager air bottles, of German manufacture.

The Chemox  is a chemical-O2, closed-circuit
apparatus with a disposable K2O2 canister. It was certified by
the USBM in 1946 as a 1-hr breathing apparatus. Because it
was certified for less than a 2-hr duration, it was considered an
auxiliary rescue apparatus. It has seen extensive use from 1946
to the present as the primary U.S. Navy shipboard firefighting
apparatus progressing from the A-1 model to the presently used
A-4. The early models had no chlorate candles and differed in
the design of the breathing bag, relief valve, and the mechanism
and procedures for loading. The U.S. Navy calls the device the
OBA, short for O2 breathing apparatus. Like the BioPak 45, it
is worn on the chest rather than the back.
K2O2 not only absorbs CO2 but also produces O2, so that a
separate O2 source is not needed. The new K2O2 canisters
contain sodium chlorate "candles," which provide a quick
source of O2, permitting the apparatus to be worn immediately.
Otherwise, the K2O2 needs three or four exhaled breaths, which
provide not only the H2O and CO2 required for the chemical
reactions, but also sufficient initial volume in the breathing bag
to permit self-contained use of the apparatus. Since there is no
O2 cylinder and gauge to indicate quantity of O2 remaining,
a timer is provided that informs the user how long the apparatus
has been in use. This allows for only a rough estimate of
remaining duration, however, since K2O2 is strictly demand responsive.
K2O2 overproduces O2 relative to human CO2
production such that the breathing bag is always full and
continually venting O2 through the volume-activated relief
valve. Earlier models had a manually activated relief valve.
The model tested was the A-4 with an automatic relief valve and
canisters containing chlorate candles.
Exhaled air goes through the exhalation check valve and
hose, through a passageway down the middle of the K2O2
canister, up through the chemical bed, and is channeled to the
bottom of one breathing bag, sweeping over the inner surface of
the bag to a connecting tube terminating at the top of the other
breathing bag. Upon inhalation, the air is drawn from the
bottom of the second breathing bag, through the inhalation
breathing hose and check valve, then back into the face mask.


Addition by Anders Puranen of Sweden;

An oxygen candel is usually potasiumchlorate being heated (>300 C):
KClO3 + heat -> KCl + 3/2 O2

This system was used in submarines for topping of oxygen levels in an emergency. Another way of doing this without the heating is to use managanesedioxid

(Mn02) as a catalyst so that the chlorate reaction can be used without the dangers of the high temp.

The system used in many portable units such as the Russin IP4 is a system where CO2 is rapidly produced upon activation by breaking a container of sulfuric acid so that it is mixed with bakingpowder making CO2

(H2S04 + K2C03 -> K2S04 + H2O + C02). This high dose of CO2 then reacts with the 'O3'-scrubber and gets the scrubber going and O2 flowing...

As far as I know the russians also use lithiumperchlorate (LiClO4) to produce O2 in their spaceprogram. This probably reacts in this way: LiCLO4

-> LiCl + 2O2

(thank you for your comments and addition)

Top of page

Please sign my Guestbook