Google "Factory Mutual Gearbox" and it seems that there are a number to choose from.

Finethread,

Thanks for the post. What is a Factory Mutual Gearbox anyway? What does that mean?

Thanks,

-Ren

Factory Mutual is an agency that provides guidance and approval for equipment that may be exposed to fire, explosion etc. Typically, if a supplier wants to market an item, such as a gear box, as explosion proof, they will hire Factory Mutual to evaluate the product and approve it.

It's similar to UL Approval.

I haven’t heard of explosion proof reducers, though, which does not mean they do not exist.

A RA may dictate you need to use fire resistant fluids (there are disadvantages associated that type of oil). The installations I have seen, utilise standard oil.

Some UG applications use water in fluid couplings in lieu of oil.

Regards,
Lyle

Gearboxes intended for use in potentialy explosive enviroments do exsist, at least they do here in Europe, Google for "ATEX regulations".
The main concern with gearboxes, pumps and other driven equipment is not so much the possibility of stray sparks generated in use, its the issue of surface temperature under fault conditions. Should the structure bcome excessively hot it may lead to auto-ignition (or flash-over) of the surrounding atmosphere.