How does a welder know if it is safe to perform work on a hollow structure? Testing of the atmosphere inside the space is critical. In several of the explosion incidents investigated by the Chemical Safety Board, it was found that testing for flammable vapors was performed in the area where the hotwork
was to be performed, on the exterior of the structure. However, the atmosphere inside the structure was never tested and the flammable gas inside the space was at explosive levels. Following these investigations they produced educational videos and a Safety Bulletin on the topic.
Sometimes the hazard isn’t caused by the object on which the welding takes place, it could be an adjacent hollow structure which has an opening into which sparks can enter and ignite flammable gases. The presence of flammable gases aren’t always obvious either. Decomposition of organic material produces several hazards, one of them being the release of flammable gases such as methane. Be sure to perform a comprehensive hazard assessment.
A space may also appear to be clean upon visual inspection and atmospheric testing but still have flammable liquids or gases lurking in attached pipes, voids under the structure, or even under sections of overlapping metal such as where a doubler plate may have been installed as a quick repair in the past.
Shipyards are in an industry which are very familiar with the dangers of hollow structures. In addition to the hazards of cargo and fuel tanks, there are many hollow structures on a ship which can pose a fire hazard. 1915.54(c) in OSHA’s shipyard standard requires a competent person to test the atmosphere of hollow structures prior to hotwork. This is normally performed by drilling a hole with an air powered drill and drawing an air sample out with a typical 4-gas meter used to test the atmosphere in confined spaces prior to entry. It is important to note that oxygen levels may be very low inside which may affect the flammable vapor concentration reading and give a false low concentration. Ensure oxygen levels are normal (20.9%) prior to determining combustible gas levels which is normally presented as a percentage of the lower explosive limit.
It is important to rely on an experienced safety professionals to assess the scenarios above and prescribe methods for eliminating the hazard. Cold cut methods instead of hotwork, inspection prior to hotwork, cleaning, purging, and inerting are all methods used by safety professionals in these scenarios. Some of the most experienced safety professionals on this subject are Marine Chemists certified by the NFPA who oversee these hazards in the maritime industry.
As I complete this article, we are just a couple days past a fire that occurred in the Gulf of Mexico on an oil platform which the Chemical Safety Board is investigating. We’ll know more as the investigation wraps up and we will learn valuable lessons to prevent similar occurances in the future. However, it appears two workers lost their lives in the incident, let’s spend the necessary time to ensure our work is done properly to prevent additional tragic incidents.
Kevin Sayler, CIH is a health and safety consultant who helps businesses increase profitability by reducing costs associated with workplace accidents, injuries and occupational diseases. He specializes in the prevention of harmful exposures to employees.
Ph: (360) 420-2985