Heptane flammability limits

Christiansen, E.W., Sung, C.J., and Law, C.K., The role of pulsating instability and global Lewis number on the flammability limit of lean heptane/air flames, Proc. Combust. Inst., 28,807,2000. 

Flammability limit 1-7% Concentrations between 1% and 7% heptane in air are flammable. Above and below these concentrations, combustion cannot be supported. 

A flammable gas detector is designed to measure the amount of flammable gas in the atmosphere and relate it to the upper and lower flammable limits. The gas mixture is drawn over a catalytic surface where oxidation, i.e. combustion, takes place. The combustion causes a rise in temperature of the surface which is measured by a decrease in its electrical resistance. The instruments have to be calibrated for the particular gas of interest but for petrol vapours pentane or heptane are used as the reference gas. The readings are usually displayed in terms of percentage of the lower explosive limit. 

Heptane is very flammable and is therefore an explosion and/or fire hazard (lower and upper explosive limits are 1.05% and 6.7%, respectively, by volume). Care should be taken to keep areas of high concentration free from ignition sources, such as sparks from static electricity, and explosion-proof equipment should be used. 

---