Explosion of Flammable Gases at a Refinery
A serious chemical accident occurred at chemical industry producing olephins and phenols. The accident resulted in injuries to several workers and extensive damage to the plant, as well as minor damage to nearby residential property. Damage to the facility was estimated at $101 million and major transportation routes were closed for several hours. The U.S. Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA) released a joint accident investigation report, (June 19, 1998) to determine the root cause and contributing factors of the accident, and to make recommendations to prevent similar accidents. In their report, EPA and OSHA determined that the immediate cause of the accident was the internal structural failure and drive shaft blow-out of a 36-inch diameter pneumatically-assisted check (non- return) valve. According to the report, the check valve's failure was due to hydrogen embrittlement and resulted in a large flammable gas leak, forming a vapour cloud that ignited.
Event Date
June 22, 1997
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
the immediate cause of the accident was the internal structural failure and drive shaft blow-out of a 36-inch diameter pneumatically-assisted Clow Model GMZ check (non- return) valve. The check valve's failure resulted in a large flammable gas leak, forming a vapor cloud that ignited.Fractography revealed typical hydrogen - embrittlement damage. Explosion energy calculation assessed the hydrogen content in the vapor cloud around 20%.The EPA/OHSA Shell report of 1998 identified these causes components:1) Inadequate Valve Design2) Failure to Learn from Prior Incidents3) Inadequate Process Hazards Analysis4) Inadequate Mechanical Integrity Measures5) Inadequate Operating ProceduresPlus the following Contributing FactorsA1) No Indication of Hydrocarbon Leak / Delayed Operator Response to LeakA2) Inadequate Communications Practices
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
check (non-return) valve,
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
Check and butterfly valves are used in refineries, petrochemical plants, chemical plants, and power generation facilities to stop and control the flow (e.g., prevent reversal of the flow's direction) of process materials through pipelines or apertures.
Consequences
Number of Injured Persons
7
Number of Fatalities
10
Currency
Lessons Learned
Lessons Learned
The valve failure which caused the accidents had various design aspects which made it unsuitable for the operation of the installation.The EPA and OSH report contains the following recommendations (for a full list see reference):1.To review process systems to determine if installed valves may be subject to a shaft blow-out hazard, and modify or replace those valves as necessary2.To consult valve manufacturers or other appropriate design authorities to ensure that any modifications made are safe.3.To update and revalidate the process hazards analysis4.To implement a more rigorous mechanical integrity inspection program for valves in extreme service 5.To develop and implement a corporate information communication system6.To implement precautionary measures contained in OSHAs PSM standard and EPAs RMP rule to prevent flammable gas leaks from resulting in vapour cloud explosions.Specific to hydrogen, the EPA stated that "valves used in hydrogen-rich or hydrogen sulfide-containing environments may be more susceptible to blow-out due to hydrogen embrittlement of critical internal components, particularly if these are made from hardened steel." (EPA enforcement Alert, 2, August 1999)
Event Nature
Emergency Action
Unknown
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
EPA & OHSA full accident investigation report
Leslie Oif, "Facilities Urged to Review Systems for Risk of Check or Butterfly Valves Safety Hazards"
Volume 2, Number 6 of "Enforcement Alert" (EPA 300-N-99-011, August 1999 ), US EPA Office of Regulatory Enforce