Fatality Case Shows Dangers of Deep Confined Spaces
An AIHce EXP 2018 session presenter analyzed a 2012 fatality inside a sewer valve vault that was 18 feet, 6 inches deep.
PHILADELPHIA -- This year's "Notable Confined Spaces" sessions on May 23 at the AIHce EXP conference, put on by the AIHA Confined Spaces Committee, included a report about one fatal incident and a discussion of how liquid hydrocarbon storage tanks with internal floating roofs can be safely entered for cleaning and maintenance.
Presenters were Bonnie Lockhart, CIH, with Ameren Corp., and Jay Gieseke, CIH, CSP, with Andeavor's St. Paul Park refinery in Minnesota.
Lockhart discussed an Aug. 28, 2012, fatal incident where a 53-year-old worker died. He was engaged in cleaning and coating surfaces inside several vertically entered confined spaces at a remote site, using the solvent MEK -- methyl ethyl ketone -- for cleaning and painting inside the spaces. At the time of the accident, one other person, a supervisor, was on site, sitting in a truck with the air conditioner running about 300 feet away from the sewer valve vault where the worker died, she said.
The worker had worked in five of the other spaces the day before, all of them 7-10 feet deep. But this vault was 18 feet, 6 inches deep, which must have surprised the worker because he had brought his 8-foot ladder to the site that day, apparently expecting the sixth space to be the same depth, she said.
When the supervisor checked on the worker, he had collapsed at the bottom of the vault. Firefighters were summoned and retrieved the fallen worker; the firefighters ventilated the space, and Lockhart said at least 1,000 air changes occurred in the space during the retrieval process.
There was no entry permit prepared, no air sampling done (either pre-entry or continuous), no attendant on duty, no retrieval equipment on hand, and no ventilation of the space conducted for the worker's entry. Two days after his death, a reading of 1,800-1,900 ppm of MEK was taken in the space, more than three times higher than the IDLH of 500 ppm for the solvent, Lockhart said.
The cause of death determined in the case was acute MEK toxicity, but Lockhart said she concluded that acute multiple solvent toxicity was the cause because the mixture he was using included other hazardous chemicals. She explained that the rungs in the side of the vault were difficult to access, and it's likely that some of his mixture spilled to the bottom as he reached for the first rungs. The victim's urine and blood indicated he'd been exposed to extremely high levels of MEK. She explained that her research, aided by personnel from an OSHA facility in Salt Lake City, showed very small amounts of MEK would produce an IDLH atmosphere at the 18-foot, 6-inch depth of the vault.
The shallower spaces were not as hazardous, but Lockhart said a witness who stopped at the site for an unrelated reason on the first day of the victim's entries said that he saw him leaning against one of the structures on the site, glassy-eyed, but assumed he may have been recovering from a hangover rather than affected by chemicals. No drugs or alcohol were found in the victim's body, she said
Gieseke discussed how workers enter large hydrocarbon tanks with internal floating roofs, including the relevant API standards, entry permits, respiratory protection worn, and lockout procedures involved. A lot of air monitoring is done inside the tanks and non-entry retrieval systems are at the ready, he said. Potential entry hazards include flammable atmospheres, H2S, benzene, hydrocarbons, static electricity buildup, NORM, and slip and fall hazards inside the tanks. After a tank is cooled and the atmosphere inside is verified to be inert, a large opening for entry is cut into the side of the tank, he explained. LOTO is ensured before entry is made. Entrants ensure an escape route is available by building cribbing to hold up the roof, which at this point is down near the bottom of the tank and is held up by many metal poles standing upright at the bottom of the tank.
A separate confined space entry permit is required to access the top of the floating roof, which at this point is about 40 feet below the rim of the tank. A tripod fall protection and retrieval system will be in place for this entry, he said.
These tanks have multiple configurations, but with proper planning and execution, the work of cleaning and maintaining them can be done safely, Gieseke said.