NFPA Journal

INTERVIEW CONDUCTED AND EDITED BY ANGELO VERZONI

Earlier this week, three workers died in the Bahamas after entering a floating metal tank used to store scrap metal at a dock. The men had been sent to clean the tank when, one by one, they entered the confined space and lost consciousness. 

“The first male did not return, the second individual [went] down to search for the first male. When he did not return, the third went down and he did not return. That caused the male from an adjacent property to come and make some inquiries and then he found three men unresponsive,” a police spokesperson told The Tribune newspaper. 

Although some local news reports have suggested the men died from exposure to chemicals or fumes in the tank, experts say it’s more likely the men actually died from a lack of oxygen. NFPA Journal recently spoke with Lawrence Russell, a principal specialist at NFPA who administers the NFPA Certified Marine Chemist Program, to discuss the common but sometimes misunderstood phenomenon of oxygen-deficient atmospheres and what can be done to protect workers in these scenarios.

RELATED: Download an NFPA fact sheet on marine confined space entry; explore more NFPA resources related to confined spaces in general; learn more about NFPA 350, Guide for Safe Confined Space Entry and Work

How do we know a lack of oxygen is likely the cause of this tragedy? 

During the emergency response, the local authorities contacted an NFPA-certified marine chemist who happened to be working in a nearby location. The chemist tested the confined space on the deck barge and reported that the tank the workers had entered had an oxygen content of 2 percent by volume. Although the medical examiner hasn’t yet determined the cause of death, based on these findings, it’s likely the men died from lack of oxygen. Normal oxygen concentration is about 21 percent by volume in air, and humans can’t survive very long when that concentration drops very low. 

What happens when you enter an oxygen-deficient space like this? 

The effects of exposure to an oxygen-deficient atmosphere are swift and can be irreversible. From the moment a person enters that space, they are effectively impaired. The oxygen content within the blood starts to drop. This affects the brain, causing a loss of coordination and impairing judgment. The person likely won’t be able to find his or her way out of the space, they’ll lose strength, fall down, lose consciousness, and could die.

This process can occur in less than 6 minutes, too, so there’s little time for rescue. 

What safeguards are in place to prevent these incidents? 

All confined spaces like the tank in the Bahamas must be tested and inspected by a competent person and a permit should be issued before anybody enters those spaces. According to OSHA and NFPA, the atmosphere of a confined space is only safe for workers when oxygen concentration is 19.5 to 22 percent by volume; the concentration of a flammable vapor in the atmosphere is less than 10 percent by volume of its lower explosive limit; any toxic materials in the atmosphere are within permissible concentrations at the time of the inspection; and the residues and chemicals remaining in the confined space aren’t capable of producing toxic material concentrations above that permissible level.

Do we know what sort of breakdown occurred that led to this most recent incident in the Bahamas? 

Not exactly. According to at least one report, though, the first worker was instructed to visually inspect the void tank from the deck of the barge but not enter it. Unfortunately, for reasons that may never be known, the worker did enter the void space, and as reported by the local news, the second and third workers went in behind him. They likely entered in an attempt to rescue the others, and it should be noted that confined space rescue should only be done by people who are trained and equipped to do so.

Do we know why the tank had such a low concentration of oxygen? 

The lack of oxygen in that space was likely caused by corrosion of steel. In other words, rust. The oxidation process by which rust forms reduces the level of oxygen in air. What some people may not understand is that entering a rusty void space can be just as deadly as entering a fuel tank or a cargo tank. No space is safe to enter until it’s been tested and determined to be safe by a competent person. An untested space is immediately dangerous to life and health.