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 CASE M8 - Oxygen Dump System, R. Johnston
Problem: Chamber O2 Overboard Dump Systems lacking differential pressure
regulators.
Symptom: Potentially hazardous pressure differential between Bibs mask and
outside ambient.
Collection of Facts: Some early O2 dump systems were installed, in
accordance with manufacturers' recommendations, without negative bias
differential pressure regulators in the exhaust line. Although no failures
have been identified, a failure of the mask vacuum regulator could result in a
potentially hazardous suction on the mask due to the pressure difference
between the chamber and ambient.
Solution: Install a negative bias differential pressure regulator in all O2
overboard dump systems and set the differential to approximately 15 psig.
CASE M9 - Materials for Oxygen System, T. Hayes
Problem: Use of Buna-N as seat material for O2 valve resulted in O2 fire.
Collection of Facts: Buna-N was used as seating material in an O2 valve.
When the valve was opened, the adiabetic heat of compression caused the Buna-N
to ignite resulting in an O2 fire.
Solution: Do not use Buna-N as seating material in O2 valves. Use Kel-F or
teflon as valve seating material.
CASE M10 - Volume of Ventilation Air - Hyperbaric, T. Hayes
Problem: It is difficult to determine the volume of air actually being used
for ventilation of a chamber.
Collection of Facts: The standard procedure is to try to calibrate the
exhaust valve using the procedure described in the U.S. Diving Manual.
Solution: Install a flow meter in the exhaust line to determine the exact
rate of ventilation.
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