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Confined Space Entry on Drilling Rigs
OSHA Hazard Information Bulletins
May 30, 1990
|MEMORANDUM FOR REGIONAL ADMINISTRATORS
Office of Field Programs
||THOMAS J. SHEPICH
Directorate of Technical Support
|| Safety Hazard Information Bulletin on Confined Space Entry on
The Directorate of Technical Support issues Hazard Bulletins (HIB)
as needed to provide relevant information regarding unrecognized or
misunderstood safety and health hazards, inadequacies of materials, devices,
techniques, and engineering controls. HIB's are initiated based on
information provided by the field staff, studies, reports and concerns
expressed by safety and health professionals, employers, and the public.
Information is complied based on a comprehensive evaluation of available
facts, literature, and in coordination with appropriate parties. HIB's do not
establish an OSHA policy.
The Marine Chemist Qualification Board of the National Fire Protection
Association (NFPA) is currently investigating two near mishaps involving
confined space entry on drilling rigs. Although this case may be outside of
OSHA jurisdiction because the Coast Guard is the principal Federal agency on
matters of safety and health on the Outer Continental Shelf, some of the case
particulars are of interest for general safety procedures in confined spaces.
The Coast Guard requires that confined spaces which have contained or are
suspected of containing flammable, combustible or toxic materials be tested
by a Marine Chemist. The Marine Chemist is then required to perform an
evaluation of the confined space environment using the guidelines of NFPA
standard 306, Standard for the Control of Gas Hazards on Vessels. If the
environment meets NFPA 306 requirements, "Safe for Workers" and/or "Safe for
Hot Work" certificates are issued. (See attached NFPA 306 excerpts.) These
requirements specify that the oxygen content of the air be between 19.5 and
22% and that the concentration of flammable materials be below 10% of the
lower explosive limit.
In the first near mishap, the Marine Chemist and two Coast Guard inspectors
were preparing to enter the final 35 feet of a 60 foot column of a mobile
offshore drilling unit. Access to this confined space was made by unbolting
a hatch door. The Chemist dropped a 25 foot testing hose attached to his MSA
Miniguard monitor into the void. The meter indicated 20.2% oxygen. Then
one inspector's Biosystems 310 Oxygen Monitor sounded an alarm. The Chemist
pumped his unit's test bulb several times and found the reading to be 8%
oxygen and dropping. The delay in receiving a proper oxygen reading could
have been created by a venturi effect of the column pulling air up from the
untested 10 feet at the column bottom.
In the second near mishap, the Marine Chemist had cleared entrance into a
bow spud can (drilling unit "foot" or base of its lattice legs) for hydrogen
sulfide exposure by noting a detector tube reading of less than 1 part per
million (ppm) An inspector entered the space wearing a Neotox hydrogen
sulfide meter. The meter's alarm sounded after 30-35 seconds with a reading
of 15 ppm. Subsequent testing by the Chemist yielded a reading of 20 ppm.
Coast Guard personnel question the Chemist's use of a 25 foot line in a 35
foot cavity and the lack of a back-up monitor. There is nothing wrong with
the use of an MSA Miniguard monitor with a 25 foot hose. It is important
that the volume of the confined space closest to the access hatch be
thoroughly checked before samples are taken at a lower level. Moreover, it
is important that the sampling be done in an as large a horizontal area as
possible at the upper regions of the space closest to the hatch. Then, after
entry, the lower depths could be examined.
The Chemist's use of a detector tube for hydrogen sulfide monitoring is
highly questionable. OSHA uses Industrial Scientific and Draeger
pump-powered monitors for such applications. The units are intrinsically
safe and have external alarms. Since the units are powered, sample hoses of
varying lengths can be employed. Moreover, three range monitors are
available that can simultaneously monitor oxygen, hydrogen sulfide and
combustibles at the lower explosive limit.
Please distribute this bulletin to all area offices, state plan states and
consultation project offices.
Page last updated: 05/03/2010