Guide to NFPA 45 Requirements for Lab Fire Protection

The NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals, is a consensus safety code that governs fire prevention and control in labs handling hazardous chemicals. It applies to any laboratory building, unit, or work area where chemicals are used or stored.

Its purpose is to protect life and property by limiting fire and explosion damage and ensuring safe egress in labs. NFPA 45 complements building codes and OSHA/EPA regulations: it adds laboratory‑specific requirements to the general fire and life safety rules.

For example, NFPA 45 defines lab "occupancy" based on chemical hazards and limits laboratory size, ventilation, and separation accordingly. Life-safety professionals and lab managers rely on NFPA 45 to design safe lab spaces; failure to comply can lead to failed inspections, fines, or shutdowns.

Fire Hazard Classifications (Class A to D)

NFPA 45 groups laboratories into four hazard classes based on the types and quantities of flammable/combustible materials they use. Each class carries different restrictions:

• Class A (High Hazard): Contains significant amounts of flammable or combustible liquids. These labs have the strictest limits on chemical quantities and layout. For example, NFPA 45 caps Class A labs at 10,000 ft² (unsprinklered) and requires extra safety measures.
• Class B (Moderate Hazard): Uses moderate quantities of flammables. Controls are less stringent than Class A but still significant. Class B labs are also generally limited to 10,000 ft².
• Class C (Low Hazard): Has only small amounts of flammables. These labs face relatively few restrictions on size or location.
• Class D (Minimal Hazard): Virtually no flammable liquids (e.g. aqueous solutions only). These labs require the least special measures.

Lab classification affects many requirements. Notably, laboratory area limits and fire separations depend on class. If sprinklers are present, Class A labs up to 10,000 ft² require 2‑hour fire walls; Class B up to 10,000 ft² need 1‑hour walls; larger A or B labs are not permitted at all. Classes C and D labs have no area limit and need no special wall separation. NFPA 45 also defines occupancy type: Class A, B, C units are treated as industrial occupancies (per NFPA 101), while Class D or instructional lab units are considered business occupancies.

Practical tip: track your chemical inventories carefully. By tallying flammable/combustible stocks, lab managers can determine their NFPA hazard class and ensure they do not exceed allowed limits.

Chemical Fume Hood Design and Use

NFPA 45 has detailed requirements for fume hoods and local exhaust. It mandates that all new or remodeled chemical fume hoods be equipped with airflow monitors alarms or flow indicators so operators know the hood is working. Hoods must be designed to contain and exhaust hazardous fumes and vapors safely; air exhausted from chemical fume hoods may not be recirculated back into the building. In practice this means hoods discharge outdoors or to a safe exhaust system. Ductless or recirculating hoods are now only allowed in very limited cases – for specific chemicals in small amounts and only with review by a qualified engineer and manufacturer approval.

NFPA 45 refers users to accepted performance guidelines for hoods. Although it does not fix an exact face velocity, ANSI/AIHA Z9.5 and OSHA recommend average face velocities around 80–120 feet/minute (fpm) (about 0.4–0.6 m/s) for typical chemical operations. The key is that airflow be sufficient to contain fumes without excessive turbulence. Best practice is to test hoods by ASHRAE 110 standards annually or after changes. NFPA 45 requires that laboratory hoods and their exhaust systems be inspected and tested at least annually. After each test, the hood must carry a dated label or log showing the last test date, average face velocity, and inspection interval. Special-use hoods (for perchloric acid, radioisotopes, etc.) must be clearly identified with signage.

Usage guidelines: Keep the hood sash at the recommended height (often marked by an airflow meter alarm); do not overload or block the baffles; and never use a hood as a storage or waste dump. By NFPA 45 rules, hoods handling flammable vapors must be on a system that maintains lab negative pressure. It's also important to ensure that hood exhaust fans are interlocked with airflow devices so the hood is disabled if ventilation fails.

Fire Suppression Systems and Extinguishers

Automatic sprinklers

NFPA 45 makes sprinkler protection mandatory for most new labs. All new laboratory units must have an approved automatic fire extinguishing system. In practice this means sprinklers per NFPA 13. Class A and B labs must be sprinklered with the ordinary hazard  design density, while Class C and D labs use the lighter Ordinary  density.

If water is a hazard for some electronics or chemicals, NFPA 45 permits an approved non-water system such as FM‑200, CO₂, or foam, designed per the relevant NFPA standard. In buildings with multiple stories, NFPA 45 also requires inside standpipe/hose systems on floors with labs.

Portable extinguishers

Every lab must also have portable fire extinguishers. NFPA 45 simply references NFPA 10: "Portable fire extinguishers shall be installed, located, and maintained in accordance with NFPA 10". In general, that means an ABC (dry-chemical) extinguisher that covers Class A/B/C fires, and a Class D (metal) extinguisher if large quantities of reactive metals like sodium, magnesium are present.

For sizing and placement, NFPA 45 says Class A labs are treated as extra-hazard areas and Class B/C/D as ordinary areas. Extinguishers must be checked monthly and undergo annual maintenance. Finally, NFPA 45 requires fire alarm coverage in Class A and B labs, typically a manual fire alarm system per NFPA 72, so that any fire in a high‑hazard lab will alert building occupants and responders.

Laboratory Ventilation and Explosion Control

NFPA 45 emphasizes continuous ventilation in chemical labs. Under Section 7, any lab unit or hood space where chemicals are present must be continuously ventilated under normal conditions to dilute flammable vapors.

In effect, lab HVAC systems should provide steady air changes and maintain the lab at a slight negative pressure relative to corridors/other areas. Critically, any chemical exhaust hoods or local devices must not recirculate back into the facility. In practice, this often means dedicated exhaust fans discharging to the roof, with intake air coming from outside or filtered sources.

NFPA 45 also defines when a laboratory is considered to have an explosion hazard. For example, a work area is classified as an explosion hazard if it involves:

• Storage or use of highly unstable chemicals;
• Large quantities of peroxides or other highly exothermic reactions;
• High-pressure reactions;
• Any conditions deemed hazardous by a qualified person.

When such hazards exist, NFPA 45 directs that "appropriate protection shall be provided", for example, vented enclosures, blast shields, or specialized explosion relief vents per NFPA 68/69

Best practices: Perform a hazard assessment before starting any new lab process. For known reactive chemistries, use fume hoods or glove boxes, and install explosion-proof switches/outlets in those areas. Avoid building up static - use grounding straps on drums, and ensure all gas cabinets and pressurized systems have proper relief valves. If lab ventilation fails, NFPA 45 suggests stopping work and securing chemicals until proper exhaust is restored.

Storage and Handling of Flammable Liquids

NFPA 45's Chapter 10 adopts the NFPA 30 classifications for liquids. Labs must limit on‑hand quantities per their hazard class.

For instance, in a Class A  lab, NFPA 45 permits up to 10 gal of Class I flammable liquids per 100 ft² of lab space and about 20 gal total of Class I/II/III combined under normal use. With approved safety cans or storage cabinets, those limits double (to 20 gal Class I, 40 gal total). Smaller labs Class B–D have proportionally lower limits, often based on 1 gal per 100 ft² or less. All flammables should be stored in approved containers: NFPA 45 limits container sizes (e.g. glass bottles of Class IA liquid must be ≤1 pt; metal/polyethylene ≤1 gal; safety cans ≤10 L).

Safe storage practices:

• Always keep flammable solvents in designated flammable storage cabinets or safety cans, and away from heat or ignition - no open flames, no hot plates within 5 ft.
• Label cabinets clearly "Flammable – Keep Fire Away".
• Avoid storing large heavy bottles above shoulder height.
• Minimize quantities: only open enough for immediate needs and replenish frequently.
• NFPA 45 also requires a written inventory of flammables in each lab to check that limits aren't exceeded.
• Under NFPA 10 and OSHA, keep at least one ABC extinguisher near the storage area.
• If Class D metals are present, use the proper Class D extinguisher.

NFPA 45 Requirements and Best Practices