This is not how your code reads. In HCFire file your code does the following:
Checks the player's inventory for Fire Suit, firefighter jacket, blacksmith apron, firefighter helmet, and welding mask.
If inventory contains Fire Suit, then it stops the code that causes burn damage early, making the player not take any damage or have any chance of being set fire.
If inventory has no Fire Suit and contains firefighter jacket/helmet then it reduces direct burn damage by 50%
If inventory has no Fire Suit and contains blacksmith apron/welding mask then it reduces direct burn damage by 75%
It then sets the chances of receiving burn damage or being set on fire. Body and head chances are calculated independently.
Kiln: 1% chance of 5 head damage, 99% no damage | 1% chance of 5 body damage, 99% no damage
Smelter: 20% chance each of 5/10 head damage, 60% no damage | 20% chance each of 5/10 body damage, 60% no damage
Blast Furnace: 20% chance each of 5/10/15 head damage, 40% no damage | 20% chance of 5/10/15 body damage, 40% no damage
Industrial Furnace: 20% chance each of 5/10/15 head damage, 40% no damage | 20% chance of 5/10/15 body damage, 40% no damage | 16% chance of being set on fire (bBurn = 3, hBurn ~= 3).
If the player receives direct burn damage then they are not set on fire, if they are set on fire they do not receive direct burn damage but are damaged by being on fire.
The welding mask and blacksmith apron reduce more damage than the firefighter hat/jacket, but none of those reduce the chance of receiving damage or being set on fire at all.
The fire suit completely negates this mechanic and prevents all possibility of burn damage or being set on fire.
Currently the industrial furnace is only used for making titanium ingots and a giant magnet. Titanium ingots have no use right now. The magnet is only used to make a large junkyard for disassembling washers, TVs, and fridges. So the industrial furnace currently does not have a huge amount of use and people realistically have a 16% chance of being set on the fire the one time they use it to make the one giant magnet they need for the one large junkyard.
In the future if you expand the use of the industrial furnace (for instance by adding recipes for titanium ingots) then I would suggest changing the code to make the firefighter gear and apron/welding mask reduce the chance of being set on fire.