Critical diameter is the minimum physical size a charge of a specific explosive must be to sustain its own detonation wave.

To determin the critical diameter a series of charges of smaller and smaller diameters are fired until difficulty in detonation wave propagation is observed.

A charge with a critical diamter more than the physical diameter of the charge will fail to maintain detonation.

A machine system which has been assessed to present unacceptable consequences if the machine or its protective system should fail.
This includes all failures or malfunctions, which could lead to danger to life or significant harm to any person or to the environment.

When emulsion explosives age the Ammonium Nitrate solution crystallises out. This occurs when the AN salts solidify and the product feel becomes gritty.

Crystallisation reduces the sensitivity of emulsions.