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This is to alert you to the danger
of fires at the interface of oxygen
regulators and cylinder valves because
of incorrect use of CGA 870 seals, and
to point out an important precaution
you can take to avoid such fires.
Background
The US Food and Drug Administration
(FDA) has received 12 reports in which
regulators used with oxygen cylinders
have burned or exploded, in some cases
injuring personnel. Some of the incidents
occurred during emergency medical use
or during routine equipment checks.
FDA and NIOSH believe that improper
use of gaskets/washers in these regulators
was a major factor in both the ignition
and severity of the fires, although
there are likely other contributing
factors.
Two types of washers, referred to as
CGA 870 seals, are commonly used to
create the seal at the cylinder valve
/ regulator interface: The type required
by many regulator manufacturers is a
metal-bound elastomeric sealing washer
that is designed for multiple use applications.
The other common type, often supplied
free-of-charge with refilled oxygen
cylinders, is a plastic (usually Nylon®)
crush gasket suitable for single use
applications.
The nylon crush gaskets require higher
torque than the elastomeric sealing
washers in order to seal the cylinder
valve / regulator interface, and if
they are used again, they require more
torque with each successive use. The
cylinder valve / regulator connection
is designed to be hand-tightened. If
the crush gaskets are re-used, the need
for increased torque may require using
a wrench or other hand tool, which can
deform the crush gasket and damage the
cylinder valve and regulator. This can
result in leakage of oxygen past the
cylinder valve seat and across the nylon
crush gasket. According to a forensic
analysis supported by FDA and the National
institute for Occupational Safety and
Health (NIOSH), "flow friction"
caused by this leakage of compressed
oxygen across the surface of the crush
gasket may produce enough thermal energy
to spontaneously ignite the nylon gasket
material.
Recommendations
FDA and NIOSH recommend that plastic
crush gaskets never be reused, as they
may require additional torque to obtain
the necessary seal with each subsequent
use. This can deform the gasket, increasing
the likelihood that oxygen will leak
around the seal and ignite.
The following general safety precautions
should also be taken to avoid explosions,
tank ruptures and fires from oxygen
regulators.
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