| Case Name |
Explosion on sampling of kerosene fractions from a tank roof |
| Pictograph |
|
| Date |
December 16, 1981 |
| Place |
Kurashiki, Okayama, Japan |
| Location |
Refinery |
| Overview |
Sampling was carried out from the roof at a propylene tetramer tank in which a combustible gas mixture should not be generated at the tank vapor layer, using a sampling thief. An explosion occurred on sampling in the tank. The hydrogen from the seal gas for pressure control of the distillation column dissolved in the propylene tetramer. It was diffused in the tank, and a combustible gas mixture was generated. Static electricity, which was charged to the sampling thief due to imperfect static electricity countermeasures, was discharged, and the combustible gas mixture exploded in the tank. |
| Incident |
A sample was taken through the gage hatch at the roof of a propylene tetramer (PT) tank in a refinery, and during sampling, an explosion occurred. The flash-point of PT was 63-64 °C. The tank temperature was much lower than the flash point temperature. PT in the tank was not regarded as being combustible.
Propylene tetramer: Within the propylene oligomer, which is polymerized using a phosphoric acid catalyst, there is a fraction that consists mainly of tetramer. It has been used as a raw material of branched-type alkylbenzene and gasoline. The name may be abbreviated to PT. |
| Processing |
Storage |
| Process Flow |
Fig2.Unit process flow
|
| Substance |
Hydrogen, Fig3 |
| Propylene Tetramer(1-Dodecene) |
| Type of Accident |
Explosion |
| Sequence |
In the PT tank, sampling was done using a sampling thief, which was suspended down through a gage hatch in the tank roof. First, the top layer sample was collected. Next, the middle layer sample was taken and the sampling thief was lifted up. An explosion occurred in the tank when the sampling thief approached the gage hatch, and two persons were injured. The tank was damaged. |
| Cause |
The two causes were pointed out. 1) Static electricity was charged at the sampling thief and the static electricity was discharged. Static electricity was generated because sampling was done by lowering and raising the sampling thief in the PT. The static electricity generated could not be discharged to the ground because the lifting string of the sampling thief was made of cotton. Therefore, it was charged on the surface of the sampler, which was a good conductor. 2) A combustible gas mixture was generated in the tank vapor layer by the effects of hydrogen. The hydrogen gas used for the distillation column reflux drum seal of the PT plant was dissolved in the PT. Hydrogen was diffused in the PT tank, and a combustible gas mixture was generated in the upper part of the tank. |
| Response |
The public fire brigade and one ambulance were on standby. A cooperative fire brigade with a 3 point set was on standby. |
| Countermeasures |
1. Seal gas of the reflux drum was changed to nitrogen.
2. The lifting strip of the sampling thief must have good conductivity, and never be electrified.
3. Sampling from the tank roof will be stopped if possible. A sampling nozzle from a circulation line or the middle level of the tank will be used if possible.
4. The operating procedure has to be clarified, and it has to be made known to everybody without exception. |
| Knowledge Comment |
Seal gas in the reflux drum of the process dissolves in a liquid, and it is diffused after rundown, and a combustible gas mixture might be generated in the tank. Attention is also necessary for seal gas in the process and inert gas should be used as seal gas. |
| Background |
1. Operators did not realize that a combustible gas mixture can be generated by diffusing hydrogen that had dissolved in the reflux drum. It is natural to predict the diffusion of dissolved gas because the pressure of the reflux drum was 60 KPaG, and that of the atmospheric tank was almost 0.0 KPaG.
2. Countermeasures against electrostatic charge were insufficient. The lifting string of the sampling thief could not discharge electricity because the string was made of cotton. The hazard of static electricity, which was generated by the sampling thief moving in a submerged state, was overlooked. |
| Incidental Discussion |
The seal gas in the atmospheric distillation column reflux drum is pressurized slightly. In the atmospheric tank, the pressure is about 0 mm at the water-column at most. The dissolved gas diffuses even at this slight pressure difference. |
| Reason for Adding to DB |
Example of explosion at a tank caused due to unexpected combustible gas-air mixture generation from accumulation of seal gas in the reflux drum |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Organizational Problems, Poor Management, Poor Operation Management, Insufficient Analysis or Research, Insufficient Practice, Lack of Imagination, Malicious Act, Rule Violation, Safety Rule Violation, Planning and Design, Poor Planning, Poor Process Design, Bad Event, Thermo-Fluid Event, Static Electricity, Secondary Damage, External Damage, Explosion, Bodily Harm, Injury, 2 person injured, Loss to Organization, Economic Loss, Manetary Damage 47 million yen
|
|
| Sources |
Fire and Disaster Management Agency, Examples of accidents at manufacturers of dangerous materials. 1981. pp.92-93.
Tokuyama City fire fighting. Outline of outdoor tank explosion.
Ministry of Labor, Safety section, Cases and countermeasures of fire and explosion disasters [A] Gas explosions and vapor explosions etc, case 9. New publication. Cases and countermeasures of labor accidents. pp.216-217(1984).
|
| Number of Injuries |
2 |
| Physical Damage |
One 1500 kL tank was damaged. Storage materials (propylene tetramer) burned. |
| Financial Cost |
¥ 47 million (Fire and Disaster Management Agency) |
| Multimedia Files |
Fig3.Chemical formula
|
| Field |
Chemicals and Plants
|
| Author |
KOBAYASHI, Mitsuo (Office K)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
|
|
