An experienced welder and his supervisor were repairing a pressurized tank at the Live Oak Cogeneration plant in Oildale (near Bakersfield) in early October. They finished their repairs on Tuesday and returned on Wednesday to test their work.

The workers were inside the tank, pressure-testing it with water and pressurized air, when something went wrong, and they were vaulted into the air. The supervisor broke an ankle; the welder suffered a fatal head injury.

Trapped in a hazardous situation

The hazards of confined spaces should not be underestimated. Employers need to ensure that all of the potential hazards of entry are identified before workers enter the space and controlled for until workers complete all job tasks and leave the space.

Hazards in confined spaces may include:

Hazards intrinsic to the space. A confined space is, by definition, a space that workers cannot get into or out of easily. That means all confined spaces pose, at a minimum, the hazard of limited egress. But other hazards may also be built into the space.

Interior configurations, like sloped bottoms or floor openings, are common intrinsic hazards. Mechanical hazards, like mixing blades, can also be present in the space and pose tripping hazards or caught in/crushed by hazards.

In the Live Oak space, a false bottom was built about 6 inches above the floor of the space. The investigation was not yet complete at press time, but this false bottom may have contributed to the hazard the workers faced.

Hazards located inside the space. Many confined spaces are tanks of some type, designed either to store or process materials. These materials can present a hazard if they remain in the space while workers perform job tasks—as when workers enter reservoirs filled with water or silos filled with grain.

Materials can also present a hazard if residue remains in an empty space, as when toxic vapors remain in a space after it is emptied, or when explosive concentrations of chemical vapor are generated from residues inside a space as a result of work performed in it.

Hazards brought into the space by workers. Workers sometimes bring hazards into the space, including heat sources, hazardous chemicals, nontoxic chemicals that can displace oxygen, electrical and mechanical hazards, and other hazards arising from the tools and materials workers use in their jobs.

In the Live Oak case, an explosive release of air from the compressed-air source the workers were using is a suspected cause of the fatal accident.

Practice tip

Let workers know which spaces are dangerous by posting signs that say "DANGER--PERMIT-REQUIRED CONFINED SPACE; DO NOT ENTER."

Safety from start to finish

Welding inside a confined space, as the workers at the Live Oak plant were doing, is extremely hazardous work. The combination of hot work, potentially explosive chemicals, toxic gases or vapors, tripping hazards, electrical hazards, and limited egress can be—and often is—deadly to workers.

But these workers had already completed their welding. The accident occurred after the part of the job that many would consider the most hazardous was complete.

Do your workers suffer a safety letdown after the most hazardous part of a job is done? Hazards can be involved in cleaning up and checking your work as well, and workers need to be safety-conscious right up until the final lock is removed. A confined space entry is not complete until:

All tools and materials have been removed from the space. Tools and materials left in the space can pose a hazard when the space is put back in service. They might react with contents that are reintroduced into the space, obstruct the movement of mechanical components inside the space, or pose other hazards.

All potentially hazardous chemical residues have been removed from the space. If chemicals were used in cleaning or repairing the tank's interior, they need to be thoroughly neutralized or removed before tank contents are reintroduced, especially if they could contaminate or react with tank contents, or if they might pose another hazard—for example, if residues could catch fire or explode when hot.

All necessary items removed from the space have been restored. If components were temporarily removed from the space—such as screens or electrical or mechanical pieces—they must be properly replaced inside the space before the job can be considered complete.