| Case Name |
Fire at a fin-fan cooler due to contamination of hydrogen by mishandling of a valve during turnaround shutdown maintenance at an atmospheric distillation unit |
| Pictograph |
|
| Date |
July 8, 1987 |
| Place |
Sendai, Miyagi, Japan |
| Location |
Refinery |
| Overview |
After turnaround shutdown maintenance of ADU was completed, a leakage was found near the overhead heat exchanger and repairs were done at reduced pressure while nitrogen was enclosing. A fire occurred when the cover was bolted using an electric wrench. The nitrogen gas supply system was rechecked because the fire was not extinguished. It was found that the connection valve that links the nitrogen gas piping to the process gas piping of the HDS was open. As the nitrogen piping used for turnaround shutdown maintenance and the combustible gas piping were connected constantly, combustible gas flowed into the nitrogen piping due to mishandling of the connection valve. It is necessary to ensure the detection of combustible gas during the hot work. |
| Incident |
During an airtight test at the final stage of turnaround shutdown maintenance of the atmospheric distillation unit (ADU), a leak was detected at the tube-attaching portion of the overhead fin-fan type heat exchanger of the main distillation column. Repair work was done with enclosing nitrogen gas. A fire occurred when the cover was bolted using an impact wrench. |
| Processing |
Manufacture |
| Individual Process |
Maintenance |
| Process Flow |
Fig2.Explanation of the accident
|
| Substance |
Hydrogen, Fig3 |
| Type of Accident |
Fire |
| Sequence |
On July 4th, 1987. Turnaround shutdown maintenance of the desulphurization unit (HDS), which was next to ADU, was completed, and nitrogen purging was conducted.
On July 5th. Shutdown maintenance of the ADU was completed.
10:00, on July 8th. An airtight test of the ADU started, and it was pressurized by steam.
11:40. A Leakage was detected near the overhead heat exchanger of the main column of the ADU. While the heat exchanger was kept at reduced pressure with enclosing nitrogen, the leakage was repaired.
16:40. Repair of leakage was completed.
17:45. A fire broke out when the cover was bolted using an electric wrench at the heat exchanger.
18:20. The nitrogen gas supply system was rechecked because the fire was not extinguished.
18:40. It was found that the connecting valve linking the nitrogen gas piping to the process gas piping in the part of recycle gas compressor of the HDS had been open. The double valve was closed.
18:55. Extinguishing was confirmed. |
| Cause |
Nitrogen gas supplied to the overhead heat exchanger was contaminated with combustible gas from the HDS. Due to a lack of communication, the connecting valves between the hydrogen piping of the HDS in operation and the nitrogen piping were opened. Hydrogen gas got mixed with nitrogen gas due to the pressure difference. |
| Response |
Extinguishing with water spraying |
| Countermeasures |
1. A check valve should be installed in the nitrogen piping.
2. The nitrogen piping connecting with combustible gas has to be connected only when it is used, or connected with double block valves and a bleeder.
3. Matters to be communicated at taking over the work should be reviewed.
4. Training on gas detection and hot work should be provided also to employees of the subcontractors. |
| Knowledge Comment |
When multiple piping for multiple purposes is connected, mishandling of valves easily causes accidents. Accidents are caused particularly frequently when utility piping is connected to process piping. Sufficient education and strict management are required. |
| Background |
In the HDS, the nitrogen piping for purging and the process gas piping were connected at two points. Workers used either connection at their own judgment. There was no communication on using nitrogen for hot work in the adjoining ADU. Therefore, the gas was generated by starting operation of the HDS flowed into the nitrogen piping due to the pressure difference, and it was ignited by a spark from an electrically-driven wrench. Communication errors between workers were identified as the main cause. However, either the defects in the operation instructions that did not specify which connection valve should be used, or insufficient education that might make workers disregard operation instructions seemed to be the genuine cause. Lack of a tense atmosphere in spite of the existence of combustibles in the adjoining unit was also considered to be a major factor. |
| Incidental Discussion |
For piping connected or separated depending on its purpose, a double block and bleeder composition may be adopted. However, from a safety point of view, it is desirable to separate piping completely by inserting a blind plate or to connect it temporarily only when it is necessary. |
| Reason for Adding to DB |
A typical accident during inspection work for turnaround shutdown. |
| Scenario |
| Primary Scenario
|
Carelessness, Insufficient Precaution, Carelessness of Operator, Organizational Problems, Inflexible Management Structure, Insufficient Information Transfer, Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Malicious Act, Rule Violation, Safety Rule Violation, Planning and Design, Poor Planning, Poor Design, Secondary Damage, External Damage, Fire, Bodily Harm, Injury, 2 person injured
|
|
| Sources |
High Pressure Gas Safety Inst. of Japan. List of accidents that occurred in 1987 related to High Pressure Gas Control. High pressure gas protection overview. p100-101(1988).
National dangerous object safety association. Generated fire during fin-fan cooler repair. One hundred cases of accidents at dangerous facilities. p13-14(1991)
High Pressure Gas Safety Inst. of Japan. Atmospheric Distillation unit. Fire in fin-fan cooler during turnaround shutdown maintenance. Accident examples of petroleum refinery and Petrochemical units. p21-26(1995)
|
| Number of Injuries |
2 |
| Physical Damage |
Slight burnout of piping attached to a fin-fan cooler. |
| Multimedia Files |
Fig3.Chemical formula
|
| Notes |
Repair |
| Field |
Chemicals and Plants
|
| Author |
WAKAKURA, Masahide (Kanagawa Industrial Technology Research Institute)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
|
