Case Ditails

Scenario
Case Name Explosion and fire on sampling at a benzene tank
Pictograph
Date January 8, 1972
Place Yokohama, Kanagawa, Japan
Location Refinery
Overview An explosion occurred at a benzene tank. Without a nitrogen seal, sampling from the tank top was carried out under a temperature condition in the explosion range without electrostatic charge prevention measures. A full-surface tank fire of a 10,000 kL tank was caused by static electricity. About 15 hours were needed to extinguish it.
Incident A full-surface fire occurred at a 10,000 kL tank of benzene on sampling through a gage hatch at the roof of the tank. The fire continued for 15 hours.
Gage hatch; A small nozzle with a lid equipped on the tank roof used to take liquid samples or measure the level with a measuring tape. The diameter of the gage hatch is usually about 20 cm (4 inches).
Processing Storage
Substance Benzene, Fig2
Type of Accident Explosion, fire
Sequence From January 5th, 1972, heating of a benzene tank started by feeding steam to a heating coil of the tank to prevent benzene from freezing. In the morning on January 8th, 38 kL of benzene was loaded into a tank car and 251 kL of benzene was received from another tank. In the afternoon of the same day, operators opened the gage hatch and measured the tank level with a metal measuring tape, and started sampling using a sampling thief. Initially, they sampled benzene at the top layer. Then, a flame blew out when they were sampling benzene at the middle layer.
Sampling thief: A device for collecting liquid material in a tank through a gage hatch. It is a metallic container with a lid. The sampling thief is dropped into the liquid suspended by a string, then the string is pulled strongly at the proper depth, the lid is opened, and the sample is taken. By drawing up the string through the gage hatch, a sample at the adequate level is taken. Static electricity is generated because the device moves in the liquid.
It is possible to take a representative sample by mixing samples at various depths.
Cause An explosion of benzene vapor in the vapor layer of a tank was caused by static electricity generated between the sampling thief and installations such as a gage hatch on sampling with the sampling thief. The ambient temperature recorded was 9.6 °C, but the liquid temperature in the tank was assumed to be 11-14 °C and a combustible gas-air mixture seems to have formed in the vapor layer. If the temperature of the liquid was high and the vapor pressure was sufficiently higher than the combustible gas-air mixture due to tank heating, it is possible for a combustible gas-air mixture to exist at the vapor layer because of the gradient of concentration in the vapor layer. Fresh air entered because the gage hatch was opened, and there was a strong possibility of a large concentration gradient. The static electricity generated by transferring benzene in the morning might have remained in the tank.
Response The fire extinguishing activity by the public fire brigade and the private fire brigade.
Countermeasures It is necessary to prevent static electricity from accumulating in the case of an inflammable fluid that easily generates static electricity. A string of a sampler must be made of brass having that is a good conductor of electricity (JIS revised after this fire). It may be necessary to mount a nitrogen blanket system at the benzene tank.
Knowledge Comment Static electricity is generated during transfer of dangerous materials. Samples should be taken after sufficient time has passed. It is necessary to carry out sampling of inflammable fluid that easily generates static electricity by a suitable method, as the method is specified in JIS, etc. Sampling from a tank roof should be avoided as much as possible. Sampling should be done from piping, etc.
Background Static electricity is always generated during sampling work from a tank roof because the sampling thief moves in the liquid. The danger of static electricity was not sufficiently recognized as there were no earths with using a cotton suspension string for the thief. Although the ambient temperature was low, the benzene tank temperature was high because of heating with steam in winter. So, a combustible gas-air mixture might have existed at a part or the entire part of the vapor layer. It is assumed that there was inadequate recognition of operating conditions.
Sequel JIS was revised after this fire. That is, the string of the sampling for the low flash point liquid must be made of brass.
Incidental Discussion Carcinogenicity of benzene is high, and sufficient countermeasures seem to be necessary for firefighting operations to avoid smoke or generated gas. However, not much attention was paid in those days.
The concentration in the vapor layer of the tank is not the same as the equivalent concentration for liquid temperature. It takes a long time to reach the same concentration even in the vapor layer. It may enter the range of an explosion, even if the liquid temperature exceeds the upper limit of an explosion, when there is a concentration gradient.
Reason for Adding to DB Example of explosion caused due to static electricity on sampling with a sampling thief from the top of a benzene tank
Scenario
Primary Scenario Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Organizational Problems, Inflexible Management Structure, Insufficient Education/Training, Ignorance, Insufficient Knowledge, Insuficient Study and Experience, Planning and Design, Poor Planning, Malicious Act, Rule Violation, Safety Rule Violation, Secondary Damage, External Damage, Explosion/Fire, Bodily Harm, Injury, 2 person injured, Loss to Organization, Economic Loss, Direct Monetary Damage 120 million yen
Sources Takeshi Yamada, Fire and explosion in benzene tank. Fire. No.86 pp.145-151(1972).
Masashi Kawasaki, Yoshiyuki Matsubara, Problems with static electricity when sampling from an oil tank., Safety engineering Vol.18 No.5 pp.284-293 (1979)
Tetsuzo Kitagawa, Explosion in benzene tank during sampling. Analysis of explosion hazard. pp.68-70 (1980).
High Pressure Gas Safety Inst. of Japan, Storage equipment. Fire and explosion when sampling at a benzene tank. Accident examples in complexes, pp.215-218(1991).
Number of Injuries 2
Physical Damage The upper part of the wall of a 10,000 kL benzene tank was destroyed by fire.
Financial Cost ¥ 120 million (Material of Chemical fire committee)
Multimedia Files Fig2.Chemical formula
Notes We should regard a tank, where the inner liquid has more than 10^10 Ω cm of specific resistance value with low ignition point and there is a combustible gas-air mixture, dangerous against static electricity.
Field Chemicals and Plants
Author KOSEKI, Hirosi (National Research Institute of Fire and Disaster)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
Scenario