How to detect, eliminate common fire hazards in cannabis cultivation operations

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(Editor’s note: This column is part of a recurring series of commentaries from professionals focused on the cannabis industry. Andrew Paris is the director of Jensen Hughes’ forensic electrical engineering practice based in Minneapolis. He specializes in investigating and consulting on electrical fires and failures, electrical system design and electrical safety.)

Fires and explosions have occurred in cannabis grow houses and processing operations for decades.

Most of these facilities were operating illegally, and they weren’t built or maintained to common electrical and fire safety standards.

Unfortunately, the lessons learned from these investigations were not well-publicized, and potential solutions were not broadly adopted.

Given the legalization of cannabis in many parts of the U.S. and throughout Canada, operators are now (rightly) paying more attention to electrical, fire and safety standards so they can mitigate risk to themselves, their employees and their property.

So, what types of safety hazards are found in marijuana grow and processing operations, and how can they be addressed to minimize risk?

Flawed electrical work

Although the quality of electrical installations by legal grow operators has increased, instances of improper electrical wiring still occur.

Some potential hazards include:

  • Bypassing the electric meter by splicing it into the service-entrance conductors. Often, this is done to avoid a high electrical bill stemming from the use of multiple high-output grow lamps. In addition to being illegal, this practice exposes the operator to a lethal-shock hazard and a potential fire hazard because of poor connections.
  • Connecting feeder and branch circuits directly to the main service lugs in the electrical panel. Installing new circuits to supply additional lamps, fans, pumps, etc., requires additional circuit breakers and/or a new electrical panel, and this can add additional costs. Bypassing this need by connecting circuits directly to the main panel lugs presents a safety hazard to the installer and a fire hazard because of the likelihood of a poor connection.
  • Improper, unprotected splices. This is a frequently encountered phenomenon. Twisting and taping connections instead of using wire nuts, splicing conductors outside of a rated junction box, putting too many conductors into a splice, etc., all expose operators to shock and fire hazards.
  • Changing out circuit breakers or fuses with higher-rated ones to prevent “nuisance” tripping. Sometimes when a circuit breaker or fuse trips because of overcurrent (i.e., too many items plugged in), operators replace it with a higher-rated one, such as replacing a 20A breaker with a 30A, rather than fixing the root cause. Instead, unplug some of the items causing the overcurrent, add a new circuit or upgrade the existing circuit.
  • Using non-UL-listed electrical system equipment or using listed equipment in the wrong way. It is best to use UL-listed or other similarly rated equipment in your electrical installations. This is also required by local and state electrical codes in most cases. Doing so ensures that your equipment has been independently tested for personal, electrical and fire safety.

An easy way to limit these hazards is to ensure your electrical installation follows National Electrical Code (NEC) provisions.

It should also be permitted, inspected and approved by the authority having jurisdiction, usually the local, county or state electrical inspector.

Poor connections

Examples of electrical connections include wire splices, terminal connections, switch contacts and power cords plugged into electrical outlets.

If a connection is poor or loose, the added electrical resistance can result in localized heating.

Eventually, the heating can increase to a point where it melts insulation and even the conductor itself, leading to hazardous electrical arcing and the ignition of surrounding combustible materials.

Hazards related to poor connections in cannabis grow operations occur most often because of poor workmanship or housekeeping issues, such as:

  • Improper electrical connections, including twisted and taped splices, instead of using approved splice connectors such as terminal blocks or wire nuts.
  • Connecting dissimilar metals, such as aluminum and copper wiring.
  • Contamination such as water, liquids, dirt or grease at plug-in connections between water circulation pumps and extension cords in hydroponic grow applications.
  • Worn extension cords or receptacle plugs can lose their internal spring tension (aka grip force) over time, leading to a loose connection when a high-wattage device is plugged in.

Proper installation methods, good housekeeping practices, the use of UL-approved, quality equipment and appropriate maintenance procedures can all decrease the possibility of a poor connection and eventual fire.

Light-fixture issues

Traditionally, marijuana grow operations have used high-power, high-intensity discharge (HID) lighting. Hazards related to HID lighting include:

  • Combustibles touching the hot lamp glass, which can easily reach over 1,000 degrees.
  • Mechanical damage that breaks the glass and allows hot particles to fall and ignite plants, plastic pots or potting material.
  • Failure and shattering stemming from oil or grease contamination (i.e., touching the lamp with your bare hands).

Other than HID lighting, full-spectrum fluorescent and LED light fixtures are also available.

Still, they have their own risks, such as installation or manufacturing defects, improper electrical connections to building wiring, incorrect building voltage supply or cheap, failure-prone ballasts or power supplies.

Another common hazard specific to fluorescent lights is the misalignment of the lamps during installation that can cause a poor connection and result in a fire.

Andrew Paris can be reached at

The previous installment of this series is available here.

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