The atmosphere in a tank is too lean if it is

 The atmosphere in a tank  is too lean if it is 

1) incapable of supporting combustion because the hydrocarbon content is below the lfl ( lower flammable limit ) 
2) capable of supporting combustion because the hydrocarbon content above the UFL upper flammable limit 
3) not safe for ballasting 

Ans________1) incapable of supporting combustion because the hydrocarbon content is below the lfl ( lower flammable limit )