Two contractors were welding atop a 10,000-gallon slurry tank when hot sparks ignited flammable vapors inside the tank, causing an explosion that killed one contractor and seriously injured another. The Chemical Safety Board (CSB) determined that the November 9, 2010 incident was caused by the increased temperature of the metal tank, sparks falling into the tank, or vapor wafting from the tank into the hot work area.
As a result, the CSB set forth new recommendations regarding “hot work”, which is defined as welding, cutting, grinding, or other spark-producing activities. Recommendations include:
- Enforce safety procedures for hot work permits and ensure explosion hazards associated with hot work activity are recognized and mitigated.
- Revise corporate procedures to require all process piping and vent piping be positively isolated before authorizing any hot work.
- Require air monitoring for flammable vapor inside tanks and other containers where hot work is to be performed.
Advanced planning, safe work procedures, and mitigation measures can help prevent tank fires and explosions caused by hot works activities. The Occupational Safety and Health Standard (OSHA), 1910.252(a)(3)(i), states that “No welding, cutting, or other hot work shall be performed on used drums, barrels, tanks or other containers until they have been cleaned so thoroughly as to make absolutely certain that there are no flammable materials present or any substances such as greases, tars, acids, or other materials which when subjected to heat, might produce flammable or toxic vapors. Any pipe lines or connections to the drum or vessel shall be disconnected or blanked.”
According to OSHA, possible mitigation measures for hot work include:
- Perform hot work in a safe location, or with fire hazards removed or covered
- Use guards to confine the heat, sparks, and slag, and to protect the immovable fire hazards.
- Do not perform hot work where flammable vapors or combustible materials exist. Work and equipment should be relocated outside of the hazardous areas, when possible.
- Make suitable fire-extinguishing equipment immediately available. Such equipment may consist of pails of water, buckets of sand, hose, or portable extinguishers.
- Assign additional personnel (fire watch) to guard against fire while hot work is being performed. Fire watchers are required whenever welding or cutting is performed in locations where anything greater than a minor fire might develop
- Monitor the atmosphere with a gas detector. If a flammable or combustible gas exceeds 10 percent of the lower explosive level (LEL), the work must be stopped. Identify the source of the gas and repair the leakage.
Although mitigation measures can limit the potential for hot work accidents, companies should create a fire pre-plan to reduce response times and improve the effectiveness of a response in the event of a fire.
For an understanding of the necessary elements in creating an effective fire pre plan, download our Fire Pre Planning Guide.