OHS Code Explanation Guide

Published Date: July 30, 2009
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Part 5 Confined Spaces

Section 52 Testing the atmospheric

Before entering a confined space that may contain a hazardous atmosphere e.g. oxygen deficient or containing toxic or explosive substances, pre-entry atmospheric testing must be done to ensure that levels of oxygen are adequate and that any hazardous substance is identified (see Figure 5.6). Competent workers must conduct the testing with suitable test equipment that has been properly calibrated and is used in accordance with the manufacturer’s specifications. It is particularly important for the individuals performing these tests to understand the limitations of the test equipment.

Figure 5.6 Atmospheric testing

After initial tests have been completed and workers are working within a confined space, periodic testing must be conducted as often as necessary to ensure the health and safety of the workers inside. The intervals at which periodic testing should occur depend on the outcome of the hazard assessment, the work being performed in the space, and the likelihood of the atmosphere changing substantially.

Situations may arise in which the atmosphere within a confined space, or the concentration of an airborne substance(s) within a confined space, can change unpredictably. If the hazard assessment identifies the potential for such a situation, then continuous atmospheric monitoring is required.

If tests identify additional hazards that were not identified in the original hazard assessment, these hazards must be addressed as required by the OHS Code. The resulting procedures and practices must be included in the code of practice so that the code of practice is complete and deals with all identified hazards.

All test results must be recorded. Employers have the option of conventional hard copy recording on paper or through some means of electronic data logging. See Table 5.3 for a list of common atmospheric hazards.

Table 5.3 Common atmospheric hazards

Common Atmospheric Hazards


How it Occurs

Why You Should be Concerned

Oxygen Deficiency (less than 19.5 percent oxygen) Chemical or biological reactions consume oxygen. Oxygen-deficient atmospheres affect heart rate, muscle coordination, and breathing. Eventually, they lead to death.

Oxygen-enriched atmospheres increase the risk of fire or explosions.
Oxygen Enrichment (greater than 23.0 percent) Results from welding task and from the improper use of oxygen for breathing air.
Flammable Atmospheres Fuel, oxygen, and a source of ignition cause fires and explosions. Flammable gases such as acetylene, butane, propane, hydrogen and methane are often common in confined spaces.

Grain. nitrated fertilizers, and ground chemicals can produce combustible dusts.
Toxic Atmospheres Accumulates through some manufacturing, biological or chemical reactions. Released during work or tasks such as welding and cleaning. Many manufacturing processes, stored materials, and work tasks produce toxic gases, vapours, or dusts.
Corrosive Atmospheres Accumulated from some manufacturing processes, biological or chemical reactions. Corrosive substances destroy living tissue. Some cause immediate damage to skin and eyes; some have no immediate effect, but cause cancer with prolonged exposure.