Mechanical vapor compression ammonia refrigeration is the refrigerant of choice in large food storage/processing plants. The refrigerant is perfectly safe when properly installed and maintained. I have worked with ammonia compression since 1970 and yes, there have been a few mishaps, explosions and fires. Once the event is investigated, they nearly always find a safety violation, improper maintenance or poorly trained operators.
I have design and started systems holding in excess of 40,000# of ammonia (NH3 or R-717).
It is nothing like an RV absorption system.
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