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COMMERCIAL SAFETY PRODUCTS |
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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 inch (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 in. (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 in. (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 3in. (7.62 cm) in diameter and the vent pipe
opening was only 1-1/4in. (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 3/4in. (1.91 cm)
schedule 80 vent stack and the relief valve be replaced with a 1/4in.
(.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 1/4in. (.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 I, Click Here)
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