There are several accepted methods for making electrical equipment safe for use in NEC Division or Zone 1 environments. Among them:
Explosion Proofing: the potentially arcing parts are encapsulated in a special housing that is designed to prevent explosions in two ways: 1. It prevents the entry of the hazardous material in potentially hazardous concentrations. 2. If hazardous materials do manage to enter the encapsulation chamber, the chamber is strong enough contain any resulting explosion or fire and prevent its spread outside the chamber to cause a secondary explosion or fire. (This method of protection is nearly the same as “flame proofing” under the IECEx and ATEX systems.)
Oil immersion: the potentially arcing (sparking) parts are submerged in oil so that the hazardous materials can not come close enough in sufficient concentration to ignite.
Sand immersion: the same idea as oil immersion except that the chamber is filled with a type of sand.
Pressurization: the potentially arcing parts are surrounded by a safe gas (usually air or nitrogen) which is pumped into the chamber where they are located in sufficient quantity and at sufficient pressure to prevent the entry of dangerous concentrations of the hazardous material.
Intrinsically safe: Worldwide, the most universally applicable approach because it is accepted under all major international standards is using intrinsically-safe voltages. The idea here is that the voltage is so low that it could not cause a spark capable of setting off an explosion or of igniting the hazardous material. The key disadvantage of this technique is that it prohibits the use of sufficient electricity to do essentially any work. As a result, it cannot operate motors, lights or most equipment.
The National Electrcial Code (NEC) of the United States allows the use of properly made motors, lights and other electrical equipment to be used in Division 1 areas. However, ATEX and IECEx codes effectively prohibit the use of electric motors in Zone 0 environments. As a result, the Division 1 classification is more flexible and recognizes that it is possible to make electrical equipment safe to do significant work in Zone 0 areas. As far as we can find, there is no record of any properly-made, installed and used Division 1 motor ever causing a fire or explosion.