LEL and HEL

[Vicky07]

Hi
Need we clarity in the LEL and HEL of gasoline . What type of instrument is required for measuring the LEL and HEL in an AIFR installed gasoline storage tank?What is the permissible limit of the levels and what will happen if the readings cross the permissible limit?
Thanks

 

[LittleInch]

To measure explosive limits you need a gas detector capable of measuring this type of vapour and outputting, normally, in % of LEL. Hence a reading of 50% means you're 50% towards getting to the lower limit. Often work stops when you get to 5% of LEL.

HEL is normally just used when you're justifying something based on the concentration of gasoline is well above the HEL and hence a hazard won't exist. However usually at some point the atmosphere needs to move from 0% ( empty, new condition) to above the HEL, so it's really a bit academeic.

No idea what AIFR is (Aluminium Internal Floating Roof?). No idea why you want to measure gasoline vapour in this space - everyone just assumes it is a Zone 0 and acts accordingly. Hence there are no "permissible levels" other than the 5% of LEL I was talking about which is the limit for doing work in a potentially explosive atmosphere. No one does work inside a storage tank which contains gasoline, even with an internal roof. Equally no one actually bothers to measure gasoline vapour inside such a space either - there's no point.

You might need to measure the vapour coming out of the tank or drifting somewhere else on site, but not in the tank itself, IMHO.

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