| Case Name |
Explosion at draw-off piping to remove hydrocarbons from liquid oxygen during changing filters at an air liquefaction separator |
| Pictograph |
|
| Date |
July 15, 1984 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Chemical factory |
| Overview |
Liquid oxygen was filled in the filter when the liquid oxygen filters were changing on the previous night. Fire occurred when residual liquid oxygen was transferred by nitrogen pressurization, after drawing off of liquid oxygen. The defects in the draw-off piping seemed to cause accumulation of hydrocarbons drawn off in the regeneration process, which reacted with liquid oxygen. |
| Incident |
The air liquefaction separator has two silica gel filters, which adsorb hydrocarbon impurities in liquid oxygen. During the regeneration process of one filter, an explosion occurred at the bottom of draw-off piping for extracting nitrogen gas from the filter. The filters were in use one after the other every one month. |
| Processing |
Manufacture |
| Individual Process |
Separation |
| Process Flow |
Fig2.Unit flow sheet
|
| Substance |
Oxygen, Fig3 |
| Type of Accident |
Explosion |
| Sequence |
Liquid drawing off work was carried out for periodic regeneration work of filters.
21:00 on July 14th, 1984. Filter A was set in the production line to collect hydrogen carbon, after it was filled with liquid oxygen.
11:30 on July 15th. Filter B for hydrocarbon collection was separated from the production line. Drawing off of liquid oxygen started by opening the lower valve of the filter.
12:45. The liquid in filter B was transferred by pressurized nitrogen supplied from a fully opened regeneration line.
21:30. The temperature was -191 °C.
22:52. Explosion occurred. |
| Cause |
Hydrocarbons separated in a regeneration process were discharged outside the system with draw-off piping for liquid oxygen. These hydrocarbons were dissolved in liquid remaining in the horizontal part of a U-tube of outlet piping. While the liquid, which was dissolving impurities such as hydrocarbons, gradually evaporated, hydrocarbons remained and concentrated. It is assumed that impurities such as concentrated hydrocarbons reacted with liquid oxygen or oxygen enriched air that was drawn out during switching of filters, and exploded in the presence of some ignition sources. |
| Countermeasures |
1. The draw-off piping for regenerated gas will be modified to make accumulation of liquids difficult.
2. The piping will be separated.
3. Drawing-off of liquid oxygen has to be ensured.
4. The flow rate of nitrogen for regeneration has to be confirmed. |
| Knowledge Comment |
On manufacturing and handling liquid oxygen, many accidents are caused due to contact with flammables. Contact between oxygen (especially liquid oxygen) and flammables should be avoided, and, if inevitable, management of ignition sources should be strengthened. |
| Background |
The piping for purging nitrogen from the filter had a specific part where the substances collected by filters such as hydrocarbons can easily accumulate. As a result, there was a possibility of liquid oxygen or oxygen enriched air contacting with impurities collected by the filter. The design of piping might also be a factor, as impurities draw-off piping and liquid oxygen draw-off piping were designed in the same way. |
| Incidental Discussion |
The danger of liquid oxygen, pure oxygen, and oxygen enriched air can be recognized through the accident. |
| Reason for Adding to DB |
A typical accident caused due to liquid oxygen |
| Scenario |
| Primary Scenario
|
Insufficient Analysis or Research, Insufficient Practice, No Imagination on Operation Condition, Poor Value Perception, Poor Safety Awareness, Insufficient Safety Measure, Planning and Design, Poor Planning, Poor Design, Usage, Operation/Use, Purge, Bad Event, Chemical Phenomenon, Oxidation, Secondary Damage, External Damage, Explosion
|
|
| Sources |
High Pressure Gas Safety Inst. of Japan. Air liquefaction separator. Explosion of draw-off piping of the hydrocarbon from filter removing hydrocarbons from the liquefied oxygen. Accident examples of Petroleum refinery and petrochemical unit. pp.156-162(1995)
|
| Physical Damage |
Draw-off piping of liquid oxygen filters was deformed. The thermometer detecting element was also deformed. |
| Multimedia Files |
Fig3.Chemical formula
|
| Field |
Chemicals and Plants
|
| Author |
WAKAKURA, Masahide (Kanagawa Industrial Technology Research Institute)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
|
