Construction Injury prevention

Close quarters

The hazards of confined spaces



Confined spaces have many unique hazards in addition to the “regular” hazards – ergonomics or struck-bys, for example – that workers may come across in a non-confined space setting.

“Our folks have seen all kinds of stuff,” said Denise Bowles, health and safety specialist with the American Federation of State, County and Municipal Employees, whose members frequently work in manholes and underground vaults. “There’s a lot of junk that ends up in there,” Bowles said, including bugs, snakes and decomposing animals.

Even typical work-related hazards can be exacerbated by the conditions inside a confined space.

“Fitting in the manhole and getting the work done can often be an issue,” said David LeGrande, health and safety director for the Communication Workers of America, headquartered in Washington.


The leading cause of death in confined spaces is asphyxiation, generally the result of oxygen deficiency or exposure to toxic atmospheres, according to OSHA. Additionally, the lack of ventilation in a confined space increases a worker’s potential for exposure to any airborne hazard, LeGrande said.

Before entering a confined space, workers should test the atmosphere for sufficient oxygen content. Blower equipment may be needed to ensure proper ventilation, LeGrande said, and AFSCME advises continuous ventilation to ensure the hazardous atmosphere does not re-form while workers are inside. However, LeGrande cautioned that blowers may not be effective in all confined spaces, such as older manholes that are deep and narrow.

Although OSHA standards specify that employers retest air levels as often as necessary, several experts who spoke to Safety+Health said workers should have continuous monitoring to ensure levels stay within a safe zone.

“With the advancement of instruments, most people ought to be able to get closer to continuous monitoring,” said Guy Colonna, division manager for industrial and chemical engineering at the National Fire Protection Association in Quincy, MA.

LeGrande warned that while low oxygen content is an expected hazard in confined spaces, hazardous chemicals such as gasoline can leach into confined spaces as well – unbeknownst to workers until they are inside the area. As an example, he pointed to manholes – hundreds of thousands exist across the country, and records on their conditions are poor. LeGrande believes manholes of particular concern are those “in concentrated geographical areas – areas with lot of people, thus a greater amount of industry and contaminants.”

But busy metropolitan areas are not the only places hazardous chemicals or substances can enter confined spaces. LeGrande said areas near gas stations may be at risk for chemicals leaching into nearby confined spaces.


Temperatures in a confined space can reach dangerous levels, especially in hotter climates and confined spaces that are metal tanks, according to Colonna.

“If you’re working in an empty steel box, which is essentially what these tanks are, they get very hot very quickly,” he said, noting that temperatures can be upward of 140° F in some situations.

To protect workers from heat stress or heat stroke, Colonna recommended instituting work-rest procedures that limit employees to 15 minutes of work in a hot enclosed space. In scenarios with extreme temperatures, work-rest procedures alone may not be the safest option – employers may need to design and install air-conditioning units to lower the temperature.


Being able to see is often an important part of getting work done. Unfortunately, “a confined space normally doesn’t come with installed overhead lighting for your convenience,” Colonna said.

As a result, additional hazards – such as slips, trips or falls – can arise. Employers should equip employees working in confined spaces with hard hats to protect their heads from inadvertent strikes.

Also, Colonna warned that not every light source is certified for a confined space environment. In an environment with a flammable atmosphere, any unapproved electrical lighting source could have unprotected circuitry. Gases and vapors can then get inside the circuitry and, when the light is turned on, ignite. Make sure any electrical lighting has been approved for use in a confined space, Colonna said.

Cramped quarters

The layout of a confined space may force workers to be careful about how they position themselves, LeGrande said.

Employees might end up in a position that makes it difficult to move while working, Colonna said, adding that even getting to the location where the work is to be conducted can be difficult and hard on the body. “You find yourself contorting your body to get to every place you might need,” he said. Employers should monitor how long workers are in such positions, and evaluate the length of time it is safe to remain there, Colonna added.


Proper lockout/tagout and hazardous energy control standards should be followed when workers are in confined spaces. Workers inside a machine such as a mixer or stirrer are vulnerable to inadvertent startups that could injure or kill them.

Colonna shared the example of an incident in which a grain inspector was aboard a ship inspecting cargo holds, and someone failed to lock out and de-energize the auger. The auger was activated, and the inspector and a terminal worker were killed.

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