Section I. GENERAL
b. The reporting of errors, omissions, and
recommendations for improving this manual by the
These instructions are for use by the operator, and by
individual user is encouraged.
Reports should be
organizational, direct support, and general support
submitted on DA Form 2028 (Recommended Changes to
maintenance personnel. They apply to the M20 oxygen-
Publications and Blank Forms) or DA Form 2028-2 (Test)
generating breathing apparatus.
located in the back of the manual and forwarded direct to
Commander, Edgewood Arsenal, ATTN: SAREA-DE-ET,
Record and Report Forms
Aberdeen Proving Ground, MD 21010.
a. Equipment maintenance forms and procedures
for their use are prescribed in TM 38-750.
Section II. DESCRIPTION AND DATA
(3) Breathing tubes. The breathing apparatus
has two flexible-rubber breathing tubes. A hose clamp
a. General. The M20 oxygen-generating breathing
fastens one end of each breathing tube to the facepiece
apparatus (OBA) (fig. 1-1) is a self-contained breathing
valve assembly; a coupling on the other end of each
device that operates independently of outside air. It is
breathing tube connects one tube to the inhalation elbow,
carried on the operator's back and will supply oxygen for
and the other tube to the plunger valve assembly.
60 minutes. To insure sufficient time for use of the OBA
in an emergency, a safe limitation of 45 minutes has been
Backplate Assembly (fig. 1-3).
established for the life of the canister. The breathing
apparatus consists of a facepiece group, backplate
(1) Guard and backplate assembly. The guard
canisters, spanner wrench, and accessories.
and backplate assembly consists of a canister guard
mounted on a backplate; the backplate is curved to fit the
b. Facepiece Group (fig. 1-2).
operator's back. A pad on the backplate provides a
cushioning support for the operator's back. Insulating
material covers the assembly and prevents heat from
(1) Faceblank. The molded rubber faceblank is
being transferred to the assembly from the canister.
available in one size and will fit most faces. Openings in
the faceblank accommodate two plastic lenses and the
(2) Bail assembly.
A bail assembly is
facepiece valve assembly. Lens clamps secure the lenses
pivotmounted on the canister guard. The assembly
in the faceblank. Integral deflectors direct air against the
consists of a bail with a jack-screw. The jack. screw
lenses to help prevent fogging. The singlepiece, rubber
contains a handwheel and a pressure plate, which secures
head harness consists of five adjustable straps and a
the canister in the canister guard.
head pad. Five buckles (two at the cheeks, two at the
temples, and one at the forehead) attach the head
harness to the faceblank.
(3) Breathing bag. The breathing bag is made of
rubber-coated fabric. It contains two rubber hoses that
(2) Facepiece valve assembly. The facepiece
are permanently cemented in place. A portion of each
valve assembly is a tubular-metal housing with an inles
hose extends outside the bag. One hose extension
branch, outlet branch, and facepiece fitting. A check valve
serves as an outlet, the other as an inlet.
is located inside each branch of the facepiece valve
connections and tabs on the bottom of the bag support
assembly. A manually operated pressure relief valve is
the breathing bag on the guard and backplate assembly.
used to release excess pressure. It is located on the inlet
branch of the facepiece valve assembly A nut and washer
(4) Inhalation elbow. An inhalation elbow is
fasten the facepiece valve assembly in the faceblank. A
housing clamp seals the junction.