Highlights •Influences of temperature and pressure on the lower flammability limit (LFL) and limiting oxygen concentration (LOC) were analyzed.•The oxidation reaction of propanal takes place slowly in the process of air injection at 95 ℃.•Oxidation reaction can be reduced by substituting the air by the mixture of 79% N2 and 21% O2 and mixing the N2 with propanal first.•With the concentration below the LFL, the unignited propanal/air still has an explosion risk after being discharged from an elevated pressure to atmospheric pressure rapidly.•LOC of propanal/N2/O2 cannot be calculated by the product of LFL and the stoichiometric oxygen/fuel ratio.