فصل 2
گازها، بخارها و مههای قابل اشتعال
منتشرشده
- LEL and UEL explained: explosive limits, %LEL and how gas detectors use them
The LEL and UEL are the lowest and highest gas concentrations in air that can burn. Learn typical values, how the %LEL scale of gas detectors works, why IEC and NIOSH figures differ, and how temperature, pressure and oxygen shift the limits.
- Flash point, autoignition temperature and minimum ignition energy: what is the difference?
Flash point tells you when a liquid makes enough vapour to burn, autoignition temperature how hot a surface must be to ignite it, and minimum ignition energy how small a spark can do it. Definitions, solvent data table and what each means in practice.
- Vapour density: which gases rise, which sink, and why it matters for detector placement
Vapour density compares a gas with air (air = 1). Methane and hydrogen rise, propane and solvent vapours sink. Cold, hot and diluted releases change the picture. How density, temperature and mixing decide where gas goes and where detectors belong.
- Flammable liquids classification under GHS/CLP and what it means for hazardous areas
GHS and EU CLP classify flammable liquids by flash point and initial boiling point into Category 1 (H224), 2 (H225) and 3 (H226); GHS adds Category 4. What the categories mean, how they map to older systems, and why handling temperature and mists decide the hazardous area.
- MESG and MIC: the two test values behind gas groups IIA, IIB and IIC
MESG is the widest 25 mm long gap that stops an internal explosion igniting the gas outside; the MIC ratio compares the smallest igniting spark current with methane's. How both tests work, the IIA, IIB and IIC limits, typical values and how mixtures are grouped.
- Hydrogen safety basics: wide flammable range, low ignition energy and invisible flames
Hydrogen burns between about 4 and 77 % vol in air, ignites with roughly a fifteenth of the energy methane needs and burns with an almost invisible flame. What these properties mean for area classification, IIC equipment, gas detection and flame detection.
- Methane, propane and LPG: properties every safety engineer should know
Natural gas (mostly methane) is lighter than air and stays a gas; LPG (propane, butane) is heavier than air and stored as a liquid that expands about 270 times. Density, LEL/UEL, T-class, gas group, odorisation, incidents and detector placement compared.
- Flammable mists and sprays: the overlooked explosion hazard
A fine spray of hydraulic oil, lube oil or fuel can explode even when the liquid is far below its flash point. How mists form and ignite, how IEC 60079-10-1 treats them, why gas detectors miss them and which measures work.
- Oxygen concentration, enrichment and inerting: how oxygen changes the explosion risk
Below the limiting oxygen concentration no flame can spread, which is the basis of inerting; above 21 % oxygen the flammable range widens and ignition becomes far easier. LOC values, inerting methods, safety margins, oxygen monitoring and enrichment hazards.