Posted By Robbie Robinson Can anyone tell me where I can find information on the acceptable %LEL for entry into aircraft fuel tanks? (JET A1) OSHA quote 10%LEL. One UK airline quotes 5%LEL. L136 (DSEAR) makes reference to keeping the LEL to 10% or below (general statement for hazardous substances). When I spoke to Exxon/Mobil they quote 0%LEL for entry into their own tanks. Many thanks for your help. Robbie.

Posted By Jane Blunt I wonder if there is a confusion here? The LEL is the lower explosive limit, and this is what the MSDS will give you. It is a material property. The document L136 is advising you to keep the concentration of vapour to a percentage of that LEL, to give you a margin of safety. Therefore, if your fluid had an LEL of 3%, keeping the vapour to 10% of the LEL would require you to keep the vapour concentration to 0.3% or less. Keeping the vapour concentration to 50% of the LEL would require keeping the vapour concentration to 1.5% or less. Jane

Posted By Guderian Normally 25% LEL is used. You will prpbably need some form of blower to vent the tank compartment. Also fully drain the tank via the aircraft drains and soak up any remaining fuel. If possible open all access panels/component mounting points to promote air flow through the tank. Depending on the aircraft you can also jack the aircraft and tilt it slightly to force fuel to the low side i.e. the side that is not been worked on. Assuming the tanks are in the structure of the wings. Full face breathing apparatus and air supply required and non metallic tools for scrapping of PRC fuel tank sealant etc. What type of aircraft are we talking - large commerical where personal access into the tanks is possible or small business jet types or fighters??

Posted By Robbie Robinson Hi Mick, Jane. MSDS only quotes LEL (0.7 for Jet A1). It does not provide information on a safe percentage of the LEL for tank entry.

Posted By MickN OK Robbie, Is there a procedure from the last time this was done? Mick

Posted By Guderian Its a standard figure used in the process industries before vessel entry. Re-read my clarification posting, entry when at 25% of the LEL % value NOT 25% of the LEL/UEL range.

Posted By tiger Please refer to AMM 28-11-00,there have detail descriptions in the Boeing Aircraft Maintenance Manual.

Posted By David Bannister Robbie, given the confusion and misunderstandings expressed on your thread I suspect you are better placed than some of the posters to answer your own query. The fuel supplier/manufacturer may give a reliable answer although the aircraft manufacturer is more likely to do so.