The definitions speak for themselves:
The Nationally Recognized Testing Laboratories-(NRTL's) Factory Mutual and Underwriters Labs-

* UL on EX- "This category covers electric battery operated trucks provided with safeguards against fire, electric shock and explosion hazards. The trucks are intended to be used in hazardous classified locations."
* UL on EE- "Type E, ES and EE industrial trucks have been classified only as to fire and electric shock hazards incident to their use in ordinary locations. No tests have been conducted to determine their suitability for use in hazardous locations as defined by the NEC." (National Electric Code)
* FM on EX - "Type EX trucks are electric-battery operated units which differ from the types E, ES, EE units. The electrical fittings and equipment are designed, constructed and assembled to permit use in atmospheres containing specifically named flammable vapors"
* FM on EE - ""Type EE trucks can be considered spark-enclosed but they are not explosion proof or dust tight and must not be used in hazardous locations requiring such equipment."
"Careful maintenance is a more than ordinary requirement for type EE trucks"

Division Definitions: (simplified)
* Division 1 -Where concentrations of hazardous material can exist or may exist.
* Division 2 -Where concentrations of hazardous material is not likely to exist.

When determining whether to use an EX or EE truck in Division 2 environments-(EE trucks are not allowed in Division 1) your customer should consider the consequences. Sample Scenario - a forklift operator using an EE truck punctures a drum in the Division 2 area. The drum begins to leak hazardous material. By virtue of the above definitions, the Division 2 area instantaneously becomes Division 1 area. As per the NFPA, the operator is supposed to turn off the EE truck and leave the area. He is to get an EX truck to remove the EE unit. In reality though, the operator will instinctively throw the truck in reverse and try to remove the forks from the punctured drum-BOOM. This is where the explosions occur, because the EE truck does not have the protective systems needed to operate in the "now" Division 1 hazardous environment.