An equation is proposed for the accurate and users friendly estimation of the lower flammability limit (M) of C/H, C/H/N, C/H/O, C/H/O/N and monohalogenated organic pure compounds in air at atmospheric Pressure in the 25-400 degrees C temperature range. The equation derived in this study used 40 chemicals (LFLs) for the derivation and over 200 for the validation. Comparisons between experimental data and estimated data show that the average absolute deviation is < 10%, and that deviations :20% are exceptions. This derived equation was validated and then used to identify erroneous LFLs in the literature. We found that Ms are in error for 10 compounds out of the 300 examined. The equation developed in this paper is compared with that developed by Britton and both equations are found to be generally consistent. Advantages and disadvantages of both equations are discussed. (c) 2005 American Institute of Chemical Engineers Process.