Gas detection requirement will differ according to the final purpose of monitoring namely: occupational safety or gas leak detection. Occupational Safety: While the occupational safety legislation might differ from region to region it is generally accepted that gases be monitored at levels expressed as Time Weighted Averages. Long term TWA gas detection may cover up to 8 hours while short term TWA gas detection may cover 10 or less minutes each time it monitors a required area. Occupational Exposure Limits (OELs) are defined by a regions authorities. Gas Leak Detection: Areas monitored for the purpose of gas leak detection will have different monitoring requirement based on the different allowable 'practical limits' for the maximum alarm threshold. 'Practical limits' refers to variable criteria depending on the gas being monitored. For example in the EU halocarbons practical limit will be set to half the concentration that can lead to adverse physical effects such as suffocation, heart sensitisation or narcotic effects. When referring to combustible gases 20% of the Lower Flammability Level (LFL) is used as a practical limit for gas concentrations. The continuous monitoring of gas concentrations is not just good practise but also a legal requirement in some industries. Concentrations of gas can be expressed in a few different and here are a few common ways: †Parts Per Million or PPM refers to the amount of parts of an element in one million parts of gas mixture. †Mass Concentration refers to the ratio of component mass to the volume of the mixture in mg/m3. †Volume composition refers to the ratio of the collective volume of all mixture components before mixing. †And lastly, LEL or Lower Explosive Limits, refers to flammable gas volumes in air. LEL is only used when measuring low concentrations of flammable gas. Different authorities will set different LEL's according to what they deem to be safe Gas Monitor operation practise, typically: Ammonia 15%, Carbon Monoxide 12.5%, Butane 1.9%, Isobutane 1.8%, LPG 1.9%, Hydrogen 4%, Methane 5.0%, Gasoline 1.4%, Toluene 1.1% and Propane 2.1%. Acceptable levels of gas detection are set on a regional basis and often referred to as Occupational Exposure Limits (OELs). For example in Europe the European Commission has established directive 2000/39/EC which requires EU member states to establish OEL's. Many regions in the EU and internationally actually refer to the UK's Health and Safety Executive Occupational Exposure Limits (Workplace Exposure Limit WELs) or to Germany's MAK values (DFG-Deutsche Forschungsgemeinschaft). In the US these standards are governed by 3 separate bodies: OSHA (Occupational Safety and Health Administration, US Department of Labour), NIOSH (National Institute for Occupational Safety, Health- US Dept of Health and Human Services), and ACGIH (American Conference of Governmental Industrial Hygienists). Additionally certain ISO standards may apply to specific situations. For example the ISO 5149 outlines standards for mechanical refrigerating systems used for cooling and heating Safety requirements. For these reasons it is best to select a gas leak detection supplier with proven practical experience relating to your industry's needs. The potential fallout for your company from choosing the wrong gas detection solution is just too big to take a chance on.
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