To limit the probability that a fire involving the parked industrial trucks will spread to the storage area, which could lead to a fire or explosion involving the ammonium nitrate, which could lead to harm to persons.
To limit the probability that ammonium nitrate will come into contact with ignition sources [e.g. hot parts] from parked industrial trucks, which could lead to a fire or explosion involving the ammonium nitrate, which could lead to harm to persons.
To limit the probability of contact between ammonium nitrate decomposition gases and exhaust gases [e.g. carbon monoxide] from internal combustion engines, which could lead to the ammonium nitrate catching fire or exploding, which could lead to harm to persons.