Fire Hazards
Although fires in hyperbaric chambers are rare, they are usually
lethal. The effects of fire at elevated ambient pressure are so devastating and
occur so fast that the fire extinguisher system may not be activated until all occupants
of the chamber have died. The very real risk of fire in hyperbaric chambers has
been illustrated by recent accidents in which chamber fires were started by a hand
warmer, a sparking toy, and other sources of ignition carried into the chamber in
the patient's clothing. Minimization of these risks involves the following:
- Control of chamber O2
concentrations (irrelevant in a monoplace
chamber)
- Minimizing the use of combustible materials within the chamber
- Controlling sources of heat and spark
- Chamber fire extinguisher system
The geometric increase in the burning rate with increases in O2
concentration mandates careful monitoring of chamber O2
, as already noted.
At increased ambient pressure, burning occurs more rapidly, even when the O2
concentration is 21%. It is important to ensure that patients do not carry cigarette
lighters, matches, battery-operated devices, or other sources of combustion into
the chamber. Cotton garments should be worn because they tend to not result in buildup
of static charges. Flameretardant materials may be of benefit, but in a monoplace
chamber they will probably burn nearly as quickly as untreated material. Excess
hair grease should be removed. Humidification of O2
within the head tent
will help minimize the risk of buildup of static electricity in hair. Hydrocarbon
lubricants (e.g., for stretcher wheels) should be scrupulously avoided because they
may spontaneously ignite on contact with aluminum in the presence of high O2
tension. Nonflammable fluorocarbon lubricants are recommended.
Sources of sparks from electrically powered equipment should be
minimized. Plugging and unplugging electrical cables during hyperbaric treatment
are a source of sparking that can be eliminated by taping all electrical plugs into
female receptacles before compression. In multiplace chambers, the flammability
of electrically powered devices (e.g., intravenous controllers) can be reduced by
purging with 100% nitrogen or helium through ports drilled in the covering at a rate
sufficient to keep the O2
concentration at a level that does not support
combustion (typically at a flow rate two to three times the internal volume per minute).
Electrical systems used in monoplace chambers must comply with specific codes that
specify the types of switches, grounding, and insulation that can be used.[145]
Volatile anesthetics in high concentration can be combustible
at 1 ATA. Brown and Morris observed that in 100% O2
, halothane up to
saturation (≅33%) in an open tube was nonflammable. In a closed tube, concentrations
of 20% to 22.5% would allow propagation of ignition. Lower halothane concentrations
propagated ignition when nitrous oxide was used as the diluent gas.[190]
Electrical sparking did not result in ignition of enflurane at concentrations up
to 5% in 100% O2
or N2
O in a closed tube at 3 ATA.[191]
Isoflurane and sevoflurane Dräger vaporizers have been used with 100% O2
up to 3 ATA, with no evidence of spontaneous combustion at room temperature. Given
the experience with halothane under hyperbaric conditions—no reported fires
and resistance to combustion in 100% O2
at 1 ATA—in the absence
of a source of ignition, it is not likely that any of the modern volatile anesthetics
pose a fire safety hazard in a hyperbaric environment.
