By James Hicks, P. Eng.
Evolve Mechanical Solutions
📞 236.777.3487

Introduction

In commercial kitchens, the exhaust fan plays a vital role in removing heat, smoke, and grease-laden vapors. However, improper installation and maintenance practices can quickly turn a safety system into a hazard. One particularly concerning issue I’ve encountered is when the grease from a rooftop kitchen exhaust fan is drained directly into a plastic bucket.

While it might seem like a quick or inexpensive solution, this setup is a serious violation of NFPA 96, the standard for ventilation control and fire protection of commercial cooking operations.

NFPA 96 Requirements

NFPA 96 provides clear, enforceable requirements for how grease must be collected and disposed of, particularly at rooftop terminations.

7.8.2 Rooftop Terminations

7.8.2.1 Rooftop terminations shall be arranged with or provided with the following:

  • (4) The ability to drain grease out of any traps or low points formed in the fan or duct near the termination of the system into a collection container that is noncombustible, closed, not rainproof, and structurally sound for the service to which it is applied and that will not sustain combustion.
  • (5) A grease collection device applied to exhaust systems that does not inhibit the performance of any fan.
  • (6) Listed grease collection systems that meet the requirements of 7.8.2.1(4) and 7.8.2.1(5).

8.1.4.6

  • Exhaust fans shall have a drain directed to a readily accessible and visible grease receptacle not to exceed 3.8 L (1 gal).

A plastic bucket used to catch grease drainage fails these requirements. It is combustible, open to weather, not rainproof, and not securely mounted— in this case it is held in place using perforated metal hanger straps (also called plumber’s tape). These thin metal bands, while commonly used for light pipe support, are not designed for structural or fire-safe applications. Over time, they can corrode, loosen, or fail, allowing the bucket to shift or spill grease directly onto the roof surface.

Common Problems Caused by Improper Grease Drainage

  1. Fire Hazard: Grease is highly flammable. A single spark or overheated fan motor can ignite an open plastic container.
  2. UV Degradation: Being exposed to sunlight, a plastic bucket deteriorates over time due to UV radiation, causing it to become brittle and eventually crack or fail. Once that happens, grease can leak directly onto the roof surface, compounding fire and environmental risks.
  3. Roof Damage: Grease degrades roofing membranes, leading to leaks, premature roof failure, and expensive repairs.
  4. Environmental and Code Violations: Allowing grease to discharge onto the roof or into an open container violates fire and environmental regulations.
  5. Attraction of Pests: Grease-laden buckets attract birds, insects, and rodents—creating sanitation and health risks.
  6. Insurance and Liability Issues: Non-compliance with NFPA 96 can void insurance coverage in the event of a fire or inspection failure.

Proper Solutions

  • Install an NFPA 96–compliant grease collection system designed specifically for rooftop use in a kitchen exhaust fan listed to ULC 762
  • Use a noncombustible, closed, and securely mounted collection container with a capacity not exceeding 3.8 L (1 gal).
  • Ensure the system does not inhibit fan performance or airflow.
  • Incorporate regular inspection and cleaning as part of your hood cleaning and maintenance schedule.
  • Keep documentation to demonstrate compliance during fire inspections and insurance audits.

Conclusion

A plastic bucket under a rooftop exhaust fan might seem like a harmless shortcut—but it’s actually a fire hazard, a code violation, and a liability risk. NFPA 96 is unambiguous: grease must be collected in a noncombustible, closed, not rainproof, and structurally sound container, no larger than 3.8 L (1 gal).

Over time, UV exposure will weaken and destroy a plastic bucket, and makeshift mounting with perforated hanger straps only adds to the risk of collapse or spillage.

If you spot a grease bucket on your roof, it’s time to take corrective action before it leads to a serious fire, roof damage, or inspection failure.