Air Quality Management in Confined Spaces

By Shockley, Brian | Occupational Hazards, September 2001 | Go to article overview

Air Quality Management in Confined Spaces


Shockley, Brian, Occupational Hazards


The hazards, regulations and atmospheric testing and ventilation solutions for confined spaces that employers should know.

On Sept. 7, 1992, a 59-year-old male barge operator entered a compartment of a stationary barge used in ice-making operations. The worker believed that the barge was not properly ballasted and was inspecting the condition of the compartment. The compartment had been sealed for approximately a year and had an oxygen concentration of less than 6 percent. The worker immediately lost consciousness and fell to the bottom of the compartment less than 11 feet below. Although rescuers quickly responded, the worker was pronounced dead upon arrival at a nearby clinic. The initial investigation and atmospheric testing indicated the extremely low oxygen content. The compartment was ventilated after the investigation and re-tested, showing an oxygen concentration of approximately 19.5 percent. (www.cdc.gov/niosh/face/stateface/ak/92-AK-036.html).

Had the confined space been ventilated prior to entry, this tragedy may not have occurred. While there are a number of other causal factors in this example (such as proper training and signage), atmospheric testing and ventilation were two safety practices that were not followed.

Air quality management is a key element in safely dealing with confined space hazards. Testing and ventilation can be the difference between life and death. This article will focus on air quality management by examining the hazards, regulations and atmospheric testing and ventilation solutions that employers should know.

What Are the Hazards?

OSHA identifies three basic types of hazardous atmospheres -- oxygen deficient (asphyxiating), toxic and flammable -- in its standard for confined spaces, 29 CFR 1910.146. While there are other aspects of confined spaces that can be considered hazardous, proper air quality management practices can identify and eliminate these three types of hazardous atmospheres.

An oxygen-deficient (asphyxiating) atmosphere is one in which there is not enough oxygen to sustain normal respiratory functions. A normal atmosphere consists of approximately 21 percent oxygen, 78 percent nitrogen and 1 percent argon, along with very small traces of other gases. Decreased levels of oxygen will cause discomfort, decreased performance, injury or even death. When the oxygen level drops below approximately 17 percent, a worker will experience an increase in breathing volume and an increased heart rate -- a hyperventilating reaction. At oxygen concentrations of 14 percent to 16 percent, a worker will experience a significantly increased heart rate, poor coordination, rapid fatigue and erratic respiration. At oxygen levels of 6 percent to 10 percent, a worker will experience nausea, vomiting, inability to function and loss of consciousness. With an oxygen level below 6 percent, there is a rapid loss of consciousness and death in minutes (Worker Deaths in Confined Spaces, NIOSH, 1994).

An asphyxiating atmosphere may occur in a confined space through the consumption of oxygen or the displacement of oxygen by another gas. Consumption of oxygen may take place during combustion of flammable materials in processes such as welding, bacterial action as in fermentation, chemical reactions as in the formation of rust and in the normal respiration of workers. Gas displacement can occur naturally. For instance, it can occur in a sewer where carbon dioxide displaces the air and reduces the oxygen concentration. Displacement can also be part of a planned safety measure. To reduce the flammability of an atmosphere, one may wish to displace the oxygen with a gas such as nitrogen, argon or helium. The American National Standard for Respiratory Protection, Z88.2-1992, recommends that any confined space containing less than 20.9 percent oxygen is to be considered immediately dangerous to life or health. This restriction is imposed because any reduction in oxygen concentrations is indicative of inadequate ven tilation. …

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