Nonstandard User Modification of Gas Cylinder Pin Indexing
Hazard [Health Devices Jul-Aug 1989;18(7-8):289-90]
A member hospital reported that a nitrous oxide cylinder was connected to
the wrong gas cylinder yoke after the hospital's machinist had modified the yoke's pin
indexing for use with cylinders containing Entonox, a mixture of oxygen and nitrous oxide
used for analgesia. However, the machinist had drilled the hole intended for the yoke's
single large pin completely through. Although some manufacturers have also made the error
of drilling pinholes all the way through the yoke, that was not the case in this incident.
When a user attempted to install the nitrous oxide cylinder, which has
holes to accept two small pins, the holes in the cylinder did not align with the yoke's
large pin. As the user tightened the screw clamp, the large yoke pin was pressed into the
large hole in the yoke; the user believed that the yoke pin was penetrating the hole in
the cylinder header. Administration of pure nitrous oxide can produce hypoxia and
subsequent death. Fortunately, the misconnection was discovered before the equipment was
used with a patient.
The Compressed Gas Association's (CGA) Standard V-1 establishes dimensions
for indexing and specifies a pin projection as well as other dimensions for the yoke.
According to the standard, the hole into which a pin is installed should be blind (i.e.,
have a specified depth). The International Organization for Standardization (ISO) Standard
407 allows through-holes for pins; however, this standard permits only those designs that
require proper mating before they can be tightened (e.g., gated yokes) and thus present no
potential for damage when the pins do not correspond to the holes. Although the hospital
machinist may have carefully positioned the hole when he made the modification in this
incident, he did not conform to the depth specification.
Conform to standard specifications in their entirety when modifying or
making gas fittings.
- Analgesia Units, Inhalation [16-953]
- Fittings/Adapters, Pin-Indexed [16-795]
- Fittings/Adapters, Pneumatic, DISS [11-727]
- Medical Gas Cylinders [16-501]
Cause of Device-Related Incident
Device factor: Improper modification
User error: Improper connection
External factor: Medical
gas and vacuum supplies
Support system failure: Lack or failure of
incoming and pre-use inspections
Mechanism of Injury or Death
Overdose; Suffocation; Underdose; Wrong drug