In the past, vehicle exhaust gas detectors have been installed on or near the ceiling. In contrary, Critical Environment Technologies Canada Inc. (CETCI) has always recommended that they be installed in the breathing zone. Recently, Quebec’s regulation has reinforced CETCI’s recommendations. It states that “dusts, gases, fumes, vapours and mists found in the workplace environment shall be measured in the respiratory zone of workers or, if this proves to be impossible owing to the lack of equipment for taking sampling in this zone, then outside the breathing zone but in a place located as close as possible to such zone” (Division V: Air Quality: 44 Methods).

The breathing or respiratory zone is defined as “the area from which the employee draws air and has been defined as being as close as possible to the nose and mouth and a hemisphere forward of the shoulders with a radius of 6 to 9 inches” (Review of ANSI/ASHRAE Standard 62.1-2004…). This is “[up to] 72” [6 ft] above the floor” (ASHRAE Standard…). The focus, of course, is on what this area contains in terms of toxins and gases and how this area can be accurately tested for safety reasons.

Gases that are heavier than air should be installed 6” from the floor. Such gases include (but not limited to) carbon dioxide, chlorine, ozone, propane, and refrigerants. Gases that are lighter than air should be installed on or near the ceiling, include (but not limited to) ammonia, methane, and hydrogen. Gases that have density close to that of air should be installed in the breathing zone, aka respiratory zone, which is 4-6 ft from the floor. Such gases include (but not limited to) carbon monoxide, carbon dioxide, oxygen, nitric oxide, nitrogen dioxide, and hydrogen sulphide.

The health and safety of individuals working near or around equipment, such as propane powered forklifts, are at risk. The exhaust is venting toxic gases, such as carbon monoxide, propane, and nitrogen dioxide, from the rear of the machine. Being in an indoor environment, the ventilation system does not know that these gases are present; therefore, cannot being diluted and / or vented outside the building. High concentrations of these fumes are extremely dangerous. At high exposure levels, they can result in death. These fumes have been linked to a number of health related issues and are a concern for the provincial health and safety boards. Having a gas detection system in place ensures that the ventilation system operates when the gas concentration level is at a dangerous level. The gas detector triggers the ventilation system to kick in and dilute the indoor air and pushes it outside the building.

For suggestions on a fixed gas detection system, please visit

Written by: Ambur Vilac, Pat Allinson & Teresa Kouch



“ASHRAE Standard: Ventilation for Accepting Indoor Air Quality”. ANSI/ASHRAE Standard 62.1-2010. 2010. Web. 20 Feb 2012. .

“Division V: Air Quality: 44 Methods.” Regulation respecting occupational health and safety. 1 May 2012. Web. 15 May 2012. .

“Guidelines Part 5 Ventilation: G5.62 Ventilation.” Occupational Health and Safety Regulation: Section 5.62. 29 October 2003. Web. 14 May 2012. .

“Review of ANSI/ASHRAE Standard 62.1-2004: Ventilation for Acceptable Indoor Air Quality – Part 2.” Workplace Hygiene. 2009. Web. 20 Feb 2012. .

“Sensor Mounting Heights & Location”. Critical Environment Technologies Canada Inc. 2012. Web. 01 June 2012. <>.