Since safety is my main function I can address this fairly easily.
There are very strict requirements for equipment to be intrinsically safe in very limited circumstances related to hazardous materials. Those situations are very specialized however so not a big deal. Think of the rest of it like this, if the environment is likely to explode, we don’t go there. We change the environment before we enter unless the circumstances are very specific.
Manufacturers may make some specialized lights for very specific cases but the vast majority of lights we buy are sold to municipalities by suppliers who oversell and over charge. We still have to buy very specific equipment for use in very specific applications. When they must do hazmat, everything changes including the radios and equipment. All the rest of our use is outside of this.
All that being said. My guys can buy whatever they want for firefighting. Our radios aren’t intrinsically safe so the lights don’t need to be either. As far as size and weight, mounting to a helmet limits both. The size of most of the 18650 single lights seems right give or take.
Our department has over 1000 members and many will buy their own lights. The ones we actually supply are dull and awkward. Fire Vulcan® LED | Firefighting Rechargeable Lantern | Streamlight®
We will supply conventional batteries AAA through D for free but I think rechargeable is the way to go. A light with a magnetic charger makes sense to me. Run time doesn’t need to be extreme as we generally win quickly or stay outside of the building. A couple hours is most of what we would work our crews. (The work is very intense.) I would think 1500-2600 lumens would be plenty with a throw type beam (Which would penetrate smoke better.) Think of something which would be a little better in fog.
I don’t know if this is something that is possible, but I do know I have looked at a lot of lights and haven’t seen much that isn’t either crazy expensive or crazy dull.
Just a thought.