Atmospheric Hazards and Air Testing

The majority of the crawl spaces in Pembina Trails contain low-hazard atmospheres. Low-hazard atmospheres are those that are known to contain clean, respirable air immediately prior to entry or when pre-entry testing is conducted. However due to unforeseen hazards such as leaking pipes, equipment, type of work or standing water in these spaces the atmosphere may change during the work activity.

There may be several different types of atmospheric hazards present in a crawl space. These hazards may already exist in the space, be brought into the space or be generated in the space during work activities. Sources of atmospheric hazards may include:

1. Previous contents of the space:  An example would be a tank with a residual amount of organic solvent in it, such as perchloroethylene.
2. Atmospheric hazards generated from chemical reactions of materials present in the space: An example would be the decomposition of organic materials that would cause the formation of methane, a flammable gas, and hydrogen sulphide, a toxic atmospheric contaminant. Another example would be rusting, or oxidation, within a confined space that would consume oxygen and cause an oxygen deficiency.
3. Activities performed in or about the space. Examples include welding, which generates welding fumes, and solvent cleaning, which generates solvent vapours.
4. Hazardous contaminants that may inadvertently enter into the space from adjacent processes or locations. An example would be carbon monoxide from vehicle exhaust entering air intakes, street manholes or trenches.
5. Low or High Oxygen - Breathable air contains 20.9% oxygen. The multi-gas detector will alarm when oxygen levels fall below 19.5%  or rise above 23%. Common causes of oxygen deficiency are:  rusting metals, combustion, displacement by other gases, microorganisms, etc. Oxygen enrichment will only occur if oxygen is pumped into a space. 
6. Carbon Monoxide -  If there is any combustion of fuel - for example, in welding, generators or equipment that is run by internal combustion engines - either inside or adjacent to the crawl space, CO may be present. The gas detector will alarm at 25 ppm. 
7. Flammable Gases and Explosives - Explosions or fires can result from gases, vapours and dusts in a crawl space. The gas detector will alarm when flammable or explosives are present in levels between 10% of the lower explosive limit (LEL) and 20% of the upper explosive limit (UEL).
8. Hydrogen Sulfide - Where there are any connections to a sewer or gas line or where any material will be rotting inside or adjacent to the space or where black stagnant standing water has accumulated, hydrogen sulfide may be present. The gas detector will alarm when H2S levels reach 10 ppm.
9. Sensitizers - May be present due to use of products such as epoxies, urethanes or isocyanate - containing paints or coatings.
10. Asbestos - May be present in the crawl space and can be found as pipe insulation, duct insulation, parging cement, etc. If you suspect damaged asbestos may be present in the space please contact your supervisor.
11. Dusts - Particularly allergenic dusts, wood dust, and grain dust - for contaminant levels and the potential for explosion.
12. Vapours - From the toxic component in cleaning products being used in the space.
13. Mold - Occurs when there is excessive moisture present in the space, flooding or high humidity due to condensation on the outside walls.

How Often is Atmospheric Testing Required?

The atmospheric testing must be done as often as necessary before and while a worker is in a confined space to ensure that acceptable atmospheric levels are maintained. The atmospheric hazards of concern include oxygen content outside the acceptable range of 19.5 to 23%, the potential accumulation of flammable, combustible or explosive agents, or accumulation of atmospheric contaminants such as carbon monoxide and methane. Testing equipment includes the use of a multi-gas detector. Pembina Trails currently uses the MSA Alt Air multi-gas detectors for atmospheric testing of its confined spaces. Gas detectors must be calibrated on a bi-weekly basis and must be bump tested every day.  Gas detectors can be booked through the safety department when required.

Where to Test the Atmosphere:

•   around the opening, before opening access to the space;
•   at locations where transfer pipes lead to the space;
•   around irregular features such as baffles, bulkheads, and sumps;
•   at locations where workers perform work;
•   at all elevations inside the space, and in those areas where gases and vapours are likely to
    accumulate.