Ask most laboratory staff about laboratory fire safety and you will get good habits: keep solvents in the cabinet, do not leave a burner unattended, know where the extinguisher is. Ask them which fire hazard classification their laboratory carries under NFPA 45 and almost nobody will know. That classification is the thing that actually governs how much solvent they may hold, what the walls around them are rated for, and whether the room needs a second exit. It is worth knowing.

Key takeaways

• NFPA 45 is the governing standard. Standard on Fire Protection for Laboratories Using Chemicals is the primary driver for most laboratory occupancies, and it adds laboratory-specific requirements on top of the general building and fire codes.
• Your laboratory has one of four fire hazard classes. Class A for high hazard through Class D for minimal, assigned on the quantity of flammable and combustible liquids in use and storage. The owner determines it, and it drives construction, sprinklers, egress and hood requirements.
• Class A allows 10 gallons of Class I liquid per 100 square feet, or 20 gallons of Class I, II and III combined. Those figures double when the liquids are kept in safety cans or listed storage cabinets.
• Container size is limited by liquid class. For Class IA liquids the largest permitted container is one pint in glass, one gallon in metal or approved plastic, and 2.6 gallons in a safety can.
• A domestic refrigerator is not a flammables refrigerator. Household units are not spark-free, and using one for solvent storage is a routine fire inspection violation. So is a hardware-store metal cabinet, which is not a listed flammables cabinet.
• No single code covers laboratory fire protection. NFPA 45 sits alongside NFPA 30, NFPA 101, the building and fire codes, and OSHA Subpart L. Editions differ, so confirm which your jurisdiction has adopted.
• Extinguisher class matters more in a laboratory than anywhere else. ABC covers most situations, Class D is needed where combustible metals are present, and the wrong agent can make a small fire considerably worse.
• Find out whether you are expected to fight a fire at all. OSHA permits an employer to require total evacuation, and many institutions now do. That is a policy question with a definite answer, and you should know yours before you need it.

The code stack, and why there is more than one

No single document covers laboratory fire protection, which is the first thing to understand about it. What applies to your building is a layered framework, and the layers can differ in their numbers.

One practical warning. Editions matter and jurisdictions adopt them at different times, so there can be substantial differences between the edition your consultant is quoting and the edition your authority having jurisdiction enforces. Confirm which edition of each document applies to your building before relying on a number from any article, including this one.

Your laboratory has a fire hazard classification

NFPA 45 requires the laboratory owner to determine a fire hazard classification based on the anticipated quantities of flammable and combustible liquids to be stored and used. There are four classes, and the consequences of the classification reach a long way beyond how much solvent sits on the shelf.

Getting the classification wrong is expensive in one direction. If an existing laboratory’s classification does not cover the work now envisioned in it, the laboratory has to be upgraded to the higher class. That typically means adding fire-rated construction to walls and replacing doors and windows, which is slow and costly. The cheaper moment to think about it is when the work is being planned, not when the inventory has already grown.

The number to know for a Class A laboratory: 10 gallons of Class I flammable liquid per 100 square feet, or 20 gallons of Class I, II and III flammable and combustible liquids combined. Both figures double, to 20 and 40 gallons, where the liquids are held in safety cans or storage cabinets. That doubling is the single strongest argument for buying proper cabinets, because it changes what the laboratory is permitted to hold.

Quantities also reduce as you go up a building. Maximum allowable quantities step down by storey above grade: Class B laboratories above the third floor are reduced by half, Class C and D on floors four to six by a quarter, and Class C and D above the sixth floor by half. If your laboratory moved upstairs during a refurbishment, the permitted inventory moved with it.

Container and storage limits

The quantity limit is not the only constraint. NFPA 45 also caps the size of individual containers, and the cap depends on the liquid class and the container material.

• Class I and Class II liquids not in use must be in safety cans or storage cabinets. Not on an open shelf, not in a fume hood, not in a cardboard box on the floor.
• Cabinets have to be listed or approved. FM approval or UL listing. A metal cupboard bought from a hardware store is not a flammables cabinet, and inspectors identify this routinely.
• No ignition sources within about five feet of flammable storage. No hot plates, no open flames. Post the area against smoking and open flames.
• Keep a written inventory. NFPA 45 requires one for each laboratory, and it is the only way to demonstrate that limits are not being exceeded. It is also the document you will wish you had after an incident.
• Dispensing has its own rules. Class I liquids in quantities under five gallons are dispensed in a chemical fume hood, or with ventilation adequate to keep accumulations below 25 percent of the lower flammable limit. Above five gallons, that moves to an inside liquid storage area. Bond and ground when transferring between metal containers.

Our guide to safe storage of combustibles works through the quantity and container tables in more detail, and chemical storage plan fundamentals covers the segregation side.

The refrigerator problem

A domestic refrigerator is one of the most reliable ways to start a laboratory fire, and it is common enough that fire inspectors list it as a routine finding. The mechanism is straightforward. A household unit has an internal light switch, a thermostat and a compressor relay, and all three make and break contact. Solvent vapour is heavier than air, so it pools in the bottom of the cabinet rather than dispersing. Sooner or later a switch arcs inside a sealed box containing a flammable atmosphere.

The fix is to use a unit built for the purpose. Laboratory-safe refrigerators relocate the switching components outside the storage compartment. Explosion-proof units go further and are built for installation in a classified area. They cost more than a domestic fridge, which is why domestic fridges keep appearing in laboratories.

Two practical points. First, check what you already have rather than assuming, because a unit inherited during a lab move is exactly the one nobody has looked at. Second, label every refrigerator explicitly for what it may and may not hold, including the ones intended for samples and the ones intended for lunch. A laboratory refrigerator with an unlabelled door is a refrigerator that will eventually contain solvent.

Extinguisher selection, which is not a single answer

Most laboratories need an ABC dry chemical extinguisher within reach, and most fires are covered by it. The exceptions are where laboratories differ from offices, and they matter because the wrong agent can turn a small fire into a much larger event.

Two laboratory-specific cautions that a general fire class table will not give you. Class D extinguishers are for burning metal, and they are not recommended for organolithium reagents. Carbon dioxide is not effective against pyrophoric reagents. Both points are covered in our guide to pyrophoric material handling, and both are the kind of detail that only appears in guidance written for laboratories.

Placement and upkeep. Under NFPA 10 and OSHA 1910.157, keep at least one ABC extinguisher near flammable storage, and a Class D unit where combustible metals are present. Extinguishers need a monthly visual check and annual maintenance, both recorded. An extinguisher with a tag showing an inspection two years ago is a finding, and more importantly it is an extinguisher nobody has confirmed will work.

• Keep 18 inches of clearance below sprinkler heads. Stacking storage into that space is a common and consequential violation, because it stops the head distributing water.
• Do not block extinguishers, alarm pulls, panels or exits. An inspector will walk the route, and so will you in the dark.

Are you expected to fight it?

This is the decision the article you are replacing does not quite make, and it deserves a direct answer. OSHA does not require employees to fight fires. Under 1910.157 an employer may elect to require total evacuation of all employees on alarm, and many research institutions and companies now do exactly that, providing extinguishers only for designated trained responders or not at all.

So the useful question is not how to use an extinguisher. It is what your organisation expects of you. There are three common positions, and you should know which one applies:

1. Total evacuation. Nobody fights any fire. Sound the alarm, leave, close doors behind you. This is increasingly the default in academic and pharmaceutical settings, and it removes the judgement call entirely.
2. Incipient stage only, trained staff. Staff who have had hands-on extinguisher training may attempt a fire that is still small, contained and not spreading, with a clear escape route behind them. Everyone else evacuates.
3. Designated response team. A named group with equipment and training responds, and everyone else evacuates.

Whichever applies, the same rules hold once you decide to leave. Sound the alarm first, because it also calls the fire service. Close doors behind you to slow spread. Do not re-enter for equipment, samples or a laptop. Account for people at the assembly point, and tell the responding crew what is in the building, because a laboratory fire is a hazardous materials call as much as a fire call. If you take one thing from this section, make it that the alarm comes before the extinguisher.

Prevention, in order of how much it actually helps

1. Reduce what you hold. The quantity of flammable liquid in the room is the dominant variable in how bad a laboratory fire becomes. Order smaller, order more often, and dispose of the half-used bottles nobody has touched in two years.
2. Store it properly. Listed cabinets and safety cans, which also doubles what you are permitted to hold. Laboratory-safe refrigerators for anything refrigerated.
3. Separate incompatibles. Oxidisers away from flammables, acids away from bases, water-reactives away from anything aqueous. A fire that starts small becomes serious when it reaches the wrong shelf.
4. Control ignition sources. Open flames only where necessary and never unattended. Keep electrical equipment out of vapour spaces, and see our guide to electrical safety in the lab for the arcing hazards that are easy to miss.
5. Use the fume hood for volatile work, and keep the sash at the certified working height. A hood removes vapour, which is the fuel.
6. Secure and separate gas cylinders. Upright, restrained, away from heat, and never near a source of ignition. Cylinders in a fire fail violently. Our guide to safe handling of compressed gas cylinders covers the detail.
7. Keep it tidy, and mean it. Clutter is fuel, blocked egress is a hazard in itself, and accumulated waste is both.
8. Use a hot work permit for any cutting, welding or brazing, including maintenance work by contractors. Hot work in a laboratory that still contains solvent inventory is a specific and well-documented cause of serious fires.

Training worth doing

• Tell people their laboratory’s fire hazard classification and what it permits. Almost nobody knows this, and it is the single piece of information that makes the quantity rules make sense rather than feel arbitrary.
• Cover the evacuation policy explicitly, including whether staff are expected to fight a fire at all. Ambiguity here is dangerous.
• Practise the walk. Where the alarm pull is, where the extinguisher is, which exit, where the assembly point is. Drills exist because people do not navigate well under stress.
• Include the response perspective. What the fire service will need to know about the building, and who provides it. A laboratory fire is a hazardous materials incident, and the crew arriving deserves better than guesswork.
• Fold it into the safety culture rather than the annual module. Our piece on fostering a lab safety culture covers making any of this stick, and PPE selection covers what people should be wearing before a fire starts.

Resources and further reading

• Making Sense of Laboratory Fire Codes (PDF). An AIChE Chemical Engineering Progress article working through NFPA 45 alongside the building and fire codes, with worked comparisons of the quantity limits each gives. The clearest public treatment of the layered framework.
• NFPA 45, 2019 edition summary. What changed from the 2015 edition, including the 20 litre container limit and the added guidance on pyrophorics and water-reactives in glove boxes. Useful for understanding why editions matter.
• 29 CFR 1910.157 — Portable fire extinguishers, including the provisions allowing an employer to require total evacuation. See also 1910.38 on emergency action plans.
• Safe storage of combustibles to avoid lab fires, our detailed treatment of the NFPA 45 quantity and container tables, and a guide to safety showers and eyewashes for the equipment that matters when someone is burned.

This article was produced under Lab Manager’s AI Editorial Guidelines