In workplaces where toxic gases can exist, gas monitoring and detection equipment plays a vital role in daily operations and safety procedures. A variety of industries - including petrochemical, agricultural, construction, mining and public works - face the challenges of routinely monitoring toxic gas levels.
Toxic gases can cause exposure-related symptoms such as dizziness, drowsiness, confusion, headaches, and in severe situations, comas and death. The risks are compounded in confined workspaces such as fuel cells, fuselage, vessels, silos, culverts and vaults.
Understanding gas detection options requires an understanding of the basics of gas monitoring as well as an awareness of the technology currently on the market.
Gas detection and calibration equipment is generally used to measure both gases and vapors. Gases expand to take the volume and shape of their container. They have one defined state at room temperature, can be compressed and can revert to a liquid state by lowering the temperature and increasing pressure. Vapors, on the other hand, are substances that are in a gaseous and liquid equilibrium at room temperature at a given pressure. Vapors can be returned to a liquid state by lowering the temperature or increasing the pressure.
Oxygen can pose a risk when either an oxygen-enriched atmosphere or an oxygendeficient atmosphere exists. The ideal oxygen concentration is 21 percent, but a range of 19.5 to 23.5 percent is considered safe. Any atmosphere with more than 23.5 percent oxygen is considered an enriched atmosphere and presents an extreme fire hazard. An atmosphere with more than 35 percent oxygen could be combustible. If oxygen levels reach 8 percent or lower, humans can experience mental failure, difficulty breathing or death in a matter of minutes. Today’s gas monitoring instruments generally sound a warning when oxygen levels reach the minimum (19.5 percent) or maximum (23.5 percent) safe levels.
Combustibles are gases or vapors that, when combined with oxygen in the free air, are flammable or explosive. For combustibles to enflame or explode, three components must be present: a fuel source (combustible gas), oxygen (air) and an ignition source (a spark or flame). These three components are referred to as the “fire triangle.” The critical point is when the gas/air mixture falls between the lower explosive limit (LEL), the concentration below which there is not enough combustible gas to support combustion, and the upper explosive limit (UEL), the concentration above which there is not enough oxygen to support combustion.
The third hazard group is toxic gases, most commonly, carbon monoxide (CO) and hydrogen sulfide (H2S). Carbon monoxide, an odorless, colorless, tasteless gas produced by burning carbon-based fuels, inhibits the flow of oxygen through the body. Hydrogen sulfide, a colorless gas with an odor like rotten eggs, can cause loss of smell and asphyxiation. Hydrogen sulfide is heavier than air, while carbon mon- oxide is slightly lighter than air. Both gases can be highly combustible. When taking samples, consider multiple sample points to make sure the results are accurate.