OSHA Hazard Information Bulletins Accidental Release of Anhydrous Ammonia at Storage/Dispensing Facilities and Elevators.
- Information Date: 19940228
- Record Type: Hazard Information Bulletin
- Subject: Accidental Release of Anhydrous Ammonia at Storage/Dispensing Facilities and Elevators.
February 28, 1994
MEMORANDUM FOR: |
REGIONAL ADMINISTRATORS |
THROUGH: |
LEO CAREY
Director
Office of Field Programs |
FROM: |
PATRICIA K. CLARK
Director
Directorate of Technical Support |
SUBJECT: |
Hazard Information Bulletin(1): Accidental Release
of Anhydrous Ammonia at Storage/Dispensing Facilities and
Elevators |
___________
FOOTNOTE(1) The Directorate of Technical Support issues Hazard
Information Bulletins (HIB) in accordance with OSHA Instruction CPL 2.65
to provide relevant information regarding unrecognized or misunderstood
health hazards, inadequacies of materials, devices, techniques, and safety
engineering controls. HIBs are initiated based on information provided by
the field staff, studies, and concerns expressed by safety and health
professionals, employers, and the public. Information is compiled based on a
thorough evaluation of available facts, and in coordination with the
appropriate parties.
The Bismarck Area Office investigated an incident of accidental release of
anhydrous ammonia at a storage/dispensing facility. The incident resulted in
the hospitalization of five people and the evacuation of 550 residents. The
unexpected release of anhydrous ammonia is believed to be due to a design
error that may have caused a 3/4" (1.91 cm) schedule 80 vent stack on the
liquid ammonia line to fail at the point where it was threaded into the
liquid ammonia line.
ANSI K-61.1-1981, Safety Requirements for the Storage and Handling of
Anhydrous Ammonia, Section 2.9.10, specifies that "A hydrostatic relief
valve or equivalent shall be installed in each section of piping between
shut-off valves to relieve pressure that could be developed by trapped liquid
ammonia." In addition, OSHA Standard 29 CFR 1910.111(c)(6)(i) requires that
all valves and other appurtenances be protected against tampering and
physical damage.
Where more than one storage tank is in use it is a common practice to plumb
both together on one manifold system. In the instance addressed here, two
30,000 gallon (113,200 liter) anhydrous ammonia storage tanks were plumbed
together on a common manifold system. A vent stack (3/4" (1.91 cm) schedule
80 pipe) with a relief valve was installed on a liquid ammonia line between
the shut-off valves on the storage tanks (See attachment). During a
replenishing operation of anhydrous ammonia from a tanker truck to one of the
two storage tanks, the vent stack with the relief valve failed resulting in
the release of approximately 12 tons (10,886 kg) of anhydrous ammonia into
the atmosphere. Investigation has determined that the 3/4" (1.91 cm) pipe
was not properly secured, putting undue strain at the point where it was
threaded into the liquid ammonia line. The strain resulted in a stress
fracture causing the vent pipe to separate from the liquid ammonia line.
The system was equipped with an excess flow valve located in the storage
tank. The valve was designed to detect a sudden drop in pressure due to the
release of ammonia through an opening equivalent to the diameter of the
liquid ammonia line and to stop its flow. The valve in this incident did not
stop the flow of liquid ammonia because the liquid ammonia line was 3" (7.62
cm) in diameter and the vent pipe opening was only 1-1/4" (3.18 cm). The
ammonia was discharged through the vent pipe opening.
It appears that the type of installation described above is common. Since
Farmland Industries of Kansas City, Missouri, installed the system involved
in the accident, the Bismarck Area Office contacted Farmland to determine the
effective means for correcting the apparent design error. Farmland Industries
recommended that the 3/4" (1.91 cm) schedule 80 vent stack and the relief
valve be replaced with a 1/4" (.64 cm) hydrostatic relief valve installed
directly into the main shut-off valve. It should be noted that the selection
and installation of relief valves should be consistent with the valve
manufacturer's specifications and recommendations.
To prevent similar accidents, it is recommended that anhydrous ammonia
facilities be informed of the potential failure of vent pipes as described
above. They should be made aware that the vent pipe on the liquid ammonia
line should be evaluated for mechanical integrity and adequacy of design. For
systems manufactured by Farmland Industries, the manufacturer recommends that
the vent pipe be removed from the liquid ammonia line, the opening plugged
and as stated in the previous paragraph, a 1/4" (.64 cm) hydrostatic relief
valve be installed directly into the main shut-off valve on the liquid
ammonia line. If, however, this cannot be done, Farmland recommends ensuring
that the vent pipe be properly secured and supported, and that a rain cap be
attached to the top of the pressure relief valve.
Furthermore, it is recommended that additional measures for safety be taken.
These measures include inspecting all other piping and appurtenances for
damage and corrosion to prevent the unexpected release of anhydrous ammonia,
and establishing an emergency plan as required in the 29 CFR 1910.38
standard, Employee emergency plans and fire prevention plans."
OSHA has not taken a position on whether this is the best approach.
Employers should be guided by the advice of qualified engineers.
Please distribute this bulletin to all Area Offices, State Plan States,
Consultation Projects and appropriate local labor and industry associations.
Attachment
(For Attachment, Click Here)
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