Reply #4: I think sodium azide is explosive around some metals

[lizerdbits]

If we ever had a buffer than had it as a small amount of preservative and it went down the sink we had to flush with LOTS of water in case the pipes were copper. I don't know what concentration it's normally used at in buffers and what would be required in a vaccine and if that reactivity would even be an issue other than spilling it on metals. I also don't know if there's any other reactivity issues either.

After typing all that I decided to look on an MSDS:

5. Fire Fighting Measures
Fire:
Combustible solid. May pose a fire hazard upon heating, shock, concussion, or friction.
Explosion:
Decomposes explosively upon heating, shock, concussion, or friction. Reacts with both copper and lead to produce explosive azides. Explosions in laboratory plumbing containing these metals is possible. Sensitive to mechanical impact.
Fire Extinguishing Media:
Water spray, dry chemical, alcohol foam, or carbon dioxide.
Special Information:
In the event of a fire, wear full protective clothing and NIOSH-approved self-contained breathing apparatus with full facepiece operated in the pressure demand or other positive pressure mode. Water spray may be used to keep fire exposed containers cool. Poisonous gases are produced in fire, including nitrogen oxides.