Sodium azide incident

The standard must be carefully chosen and it should ideally possess the following properties have a simple spectrum with very few bands be stable to heat and not absorb moisture be easily reduced to a particle size less than the incident radiation without lattice deformation be non-toxic, giving clear discs in a short time be readily available in the pure state. Some common standards used include calcium carbonate, sodium azide, napthalene and lead thiocyanate. 

INCIDENT 3.2.2.1 DIMETHYL SULFATE AND SODIUM AZIDE EXPLOSION ... 

During the preparation of methyl azide from dimethyl sulfate and sodium azide, an explosion occurred. The same reaction had previously been carried out without incident. Upon investigation, the chemists found that Bretherick s Handbook of Reactive Chemical Hazards reported that this reaction can result in an explosion if the acidity of the solution drops to pH 5. It was surmised that sodium hydroxide, which was added to maintain the pH above 7, was not added at a sufficient rate to keep the solution at the required pH. Further steps (visible color indicator) were taken in subsequent preparations to ensure that the pH was maintained in the appropriate range. 

---