Hazardous gas detection systems

Summary of the most important definitions related to gasometry:

• potentially explosive atmospheres: Space in which explosive gas atmospheres may occur (there is a potential hazard).
• explosive gas atmosphere: Mixture of combustible substances in the form of gas, vapour or mist with air under atmospheric conditions in which, when ignited, the combustion spreads over the entire unburned mixture.
• lower explosive limit (LEL): Volumetric concentration of a combustible gas or vapour in the air below which no explosive gas atmosphere may be expected to occur.
• upper explosive limit (UEL): Volumetric concentration of a flammable gas or vapour in the air above which no explosive gas atmosphere may be expected to occur.
• self-ignition temperature of an explosive gas atmosphere: The lowest heated surface temperature at which, under the conditions laid down in accordance with IEC 79-4, flammable substances may ignite in the form of a mixture of gas, vapour or mist and air.
• explosion proof enclosure type: Specific countermeasures applied to electrical equipment to avoid ignition of the surrounding explosive gas atmosphere.
• occupational exposure limit (OEL): The weighted average value of concentration, the impact of which, on an employee during an 8-hour daily and average weekly working time specified in the Labour Code, during his/her professional activity, should not cause negative changes in his/her health condition and in the health condition of future generations.
• short-term exposure limit (STEL): Average concentration value that should not cause adverse effects on workers’ health if it occurs in the working environment for no more than 15 minutes and no more than twice during a shift, with an interval of no less than one hour.
• ceiling exposure limit (C): A concentration value which, due to risk to the health or life of a worker, may not be exceeded at any time in the working environment.