Some of accidents are based on unstable chemical substances. These chemicals are easily decomposed or Ignited by heats or mechanical shocks like sodium azide. Sodium azide is commonly used as propellant for inflating automotive safety bags and the other chemical manufacturing purposes. The investigation of thermal hazard potential of sodium azide is very important because unexpected traffic accident can be occureed. The experiments were carried out by DSC, TG an ARC in air, oxygen, argon and nitrogen atmosphere. The decomposition temperatures were about $410^{circ}C$~$420^{circ}C$ by DSC and $330^{circ}C$~$370^{circ}C$ by ARC, this is very significant result for treatment of chemical. The heats of decomposition were about 81 kcal/mol in ai. and 10 kcal/mol in other atmosphere.