Is the toxic effect of ammonia a larger risk than the risk on explosion?

Quite often we get the question whether it is necessary to classify ammonia storage vessels and pump rooms into hazardous areas. Many people think that it’s not needed because the toxic effect of ammonia starts at low concentrations (ppm) far below the lowest explosion limits (vol%), and thus the toxic effects are a higher risk than explosion risks. And preventive measures to reduce the risks of toxic effects for human (e.g. PID sensors, warning lights, procedures) will also reduce the risk of explosions.

Although measures to reduce the risk of the toxic effects may also reduce the risk of the effects of explosions to humans ( because people should not enter a pumproom when the alarm, that detects a spill, is on), the probability of an explosion is certainly not reduced by these kind of measures.The vapor pressure of ammonia is quite high and therefore a spill will lead to a large amount of evaporation. When a non-ex certified pumpkid in the vicinity of the spill fails and leads to a spark or a high surface temperature, these vapors can be ignited and cause a fire or an explosion. So always assess ammonia storage and or pump facilities for hac.

Hazcalc is easy to use for that: