Walked into a strip mall buildout a while back where the general contractor had already screwed two 5 lb ABCs to the wall before anybody who does fire protection got a call. Wrong spots, wrong size for the kitchenette in back, and one of them was mounted so the top of it cleared 6 feet off the slab. None of that is dramatic. It's also all wrong, and it's the kind of wrong that gets caught on a final and pushes a punch list two more weeks. So here's the travel distance and placement stuff the way I actually use it on a job, not the way the pamphlet reads.
The 75 foot number, and what it's really measuring
For Class A hazards (ordinary combustibles, offices, retail, most of what you'd call "light hazard" occupancy), NFPA 10 caps travel distance at 75 ft. That's not a straight line from the extinguisher to the far wall. It's the actual path a person walks, around the shelving, through the doorway, down the aisle. I've seen designers measure it as the crow flies and get burned when the AHJ walks it with a wheel.
Minimum rating matters too, usually 2-A for light hazard, higher for ordinary hazard occupancies (think a woodshop or a warehouse with denser combustible loading). Check your hazard classification before you pick the can. I think a lot of techs just grab whatever's cheapest at the supply house and that's backwards.
Class B doesn't get one number, it gets two
This is the part that trips people up. Class B hazards (flammable liquids, that back room with the solvent drums or the paint booth) don't ride the 75 ft rule at all. NFPA 10 splits it by hazard size:
- Smaller hazards, rated 5-B or 10-B, get 30 ft max travel distance.
- Larger hazards, 20-B up through 80-B, get 50 ft.
So a little parts washer versus a real flammable liquid storage area can call for a completely different spacing plan, even in the same building. I'd rather over rate the extinguisher and keep the shorter distance than argue about which bucket a hazard falls into on inspection day.
Class K lives close to the grease, full stop
Cooking appliances using vegetable oils or animal fats need Class K protection, and it has to be within 30 ft travel distance of the hazard. In practice I never push it anywhere near that far. If there's a hood system and a fryer line, the K goes on the wall right at the edge of the cook line, close enough that nobody has to think about where it is when something's already on fire. Don't quote me on every AHJ's local amendment here, some jurisdictions want it even tighter or want it paired with specific hood suppression sign off, so check before you finalize a kitchen layout.
Mounting height, the thing that actually gets measured on a final
Weight decides this one:
- 40 lbs or less: bottom of the extinguisher at least 4 inches off the floor, top no higher than 5 ft.
- Over 40 lbs: top no higher than 3.5 ft.
I've failed a final over this exact thing, an extinguisher hung a few inches too high because whoever mounted it eyeballed it at a comfortable reach height instead of measuring. Bring a tape measure to the walkthrough. Sounds obvious, half the crews don't.
Signage and obstruction, the quiet failure point
If the extinguisher isn't visible from the normal path of travel, meaning shelving, a rack, a partition wall blocks the sightline, you need a sign or a marker indicating its location. I've had reviewers reject a set for exactly this on a warehouse job where the extinguisher itself was code compliant but you couldn't see it from more than ten feet away because of pallet racking. The rule isn't really about the can, it's about somebody finding it fast under stress.
A worked layout: strip mall unit with a small kitchen
Take a roughly 2,400 sq ft unit, retail floor up front, a small prep kitchen with two fryers in back, and a storage closet with some cleaning solvents. Here's how I'd lay it out and why:
| Location | Hazard class | Extinguisher | Travel distance target | Mount height |
|---|---|---|---|---|
| Front retail floor, near entrance | Class A (light hazard) | 5 lb 2A:10B:C | 75 ft max | top at 5 ft |
| Rear of retail, near hallway to kitchen | Class A (light hazard) | 5 lb 2A:10B:C | 75 ft max | top at 5 ft |
| Cook line, edge of hood system | Class K | 6 L wet chemical | within 30 ft of appliances | top at 5 ft |
| Storage closet, solvent shelf (10-B rated hazard) | Class B | 10 lb 4A:60B:C or 10-B rated dry chem | 30 ft max | top at 3.5 ft (over 40 lb unit) |
Two Class A units cover the whole retail floor without either one exceeding 75 ft of travel from any corner. The K sits right at the grease, no debate about distance. The B unit in storage is sized and placed for the smaller hazard rating rather than assuming the bigger 50 ft allowance, because I'd rather the number work no matter which side of that hazard line the AHJ decides to put it on.
Anyway. None of this is complicated once you've done it a dozen times, it's just a lot of small numbers to keep straight across one submittal, and I've absolutely mixed up a mounting height while doing five units back to back. Full disclosure, I built FireDeck partly because keeping that kind of detail consistent across every device on a job got old, though extinguisher placement itself is still something you walk and measure by hand.