the apparatus, the ambient atmospheric pressure (service life is cut in half by a doubling
of the atmospheric pressure), and workload. A warning device shall be provided to
indicate to the wearer when the service life has been reduced to a low level. Some
SCBA devices have a short service life (few minutes) and are suitable only for escape
(self rescue) from a non-respirable atmosphere. Chief limitations of SCBA devices are
their weight or bulk or both, limited service life, and the training required for their
maintenance and safe use.
(b) Closed circuit apparatus. The closed circuit operation conserves
oxygen and permits longer service life.
(c) Open circuit demand and pressure demand. The demand type
produces a negative pressure in the face piece on inhalation whereas the pressure
demand type maintains a positive pressure in the face piece and is less apt to permit
d. Supplied-Air Respirators.
(1) Description. Supplied-air respirators include all completely assembled
respirators designed for use during entry into or escape from hazardous atmospheres.
The respirable air supply in not limited to the quantity an individual can carry, thus the
devices are lightweight and relatively simple.
(a) Type "A" supplied air respirator. A hose mask respirator for entry
into and escape from atmospheres not immediately dangerous to life or health which
consist of a motor driven or hand operated blower that permits the free entrance of air
when the blower is not operating, a strong large diameter hose having a low resistance
to airflow, a harness to which the hose and the lifeline are attached and a tight fitting
(b) Type "B" supplied air respirator. A hose mask respirator, for entry
into and escape from atmospheres not immediately dangerous to life or health, which
consists of a strong, large diameter hose with low resistance to airflow through which
the user draws inspired air by means of his lungs alone, a harness to which the hose is
attached, and a tight fitting face piece.
(c) Type "C" supplied air respirator. An airline respirator, for entry into
and escape from atmospheres not immediately dangerous to life or health, which
consists of a source of respirable breathing air, a hose, a detachable coupling, a control
valve, orifice, demand valve or pressure demand valve, an arrangement for attaching
the hose to the wearer, and a face piece, hood, or helmet.
(d) Types "AE," "BE," and "CE" supplied air respirators. Types "A," "B,"
or "C" supplied-air respirator equipped with additional devices designed to protect the
wearer's head and neck against impact and abrasion, and with shielding material to