The Hazards of Grow Houses


The environment favorable for growing marijuana indoors can be a very dangerous environment for firefighters when a fire occurs in a “grow house.” The term “grow house” is misleading because it implies that marijuana growing occurs only in detached private dwellings, which is hardly the case. For example, one or two rooms in apartments are commonly converted to a grow house to produce a small crop. Conversely, some of the largest and most productive grow houses are located in rented warehouse bays (photo 1). For this article, a grow house refers to any indoor marijuana-growing operation.

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(1) This grow house, located in a rented warehouse bay, is essentially a wood-frame shack built inside a Type II noncombustible building. This enclosure is oxygen deficient because of the use of carbon dioxide from cylinders to hasten the growth of the plants. (Photos by Eric Goodman.)

Growing operations are replete with electric hazards because of exposed wiring, terminals, and connections. Artificial light is created by high-voltage mercury vapor or high-pressure sodium lamps, each requiring its own igniter, capacitor, and transformer (photo 2). Firefighters risk electrocution if they make bodily contact with a metal tool or direct a stream of water on this equipment at close range. The risk for electrocution is intensified when firefighters operate in limited visibility, which may not be improved by a thermal imaging camera (TIC), because the ceilings and walls are commonly covered with reflective insulation board. The reflective surface acts as a mirror when viewed through a TIC (photo 3). All but the smallest growing operations require a substantial amount of electricity to illuminate the high-intensity lights and run the air-conditioners necessary to remove the excessive heat produced by the lights. The power is commonly obtained by illegally and dangerously tapping into the electric service before the electric meter (photo 4). This diversion of the electrical service is usually connected to separate electrical panels specifically for the grow operation (photo 5). The theft of electricity and makeshift wiring make it almost impossible for firefighters to ensure that the power has been shut off.

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(2) Each high-intensity lamp requires its own capacitor, which holds an electrical charge after power is shut off, and a transformer, to step up voltage.

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(3) Light from high-pressure sodium vapor lamps reflects off the walls and ceilings. The reflective surface acts as a mirror when viewed through a thermal imaging camera.

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(4) The wire just below the back of the weatherhead taps into the electrical service before the electric meter. [Photos courtesy of Miami-Dade (FL) Fire Rescue.]
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(5) Illegal diversion of electric service is usually connected to separate panels specifically for the grow operation. Theft of electricity and makeshift wiring make it almost impossible to ensure that the power is disconnected.

Grow houses are extensively insulated to increase the efficiency of air-conditioning and to reduce heat transfer to the upper floors and attic. Foil-covered insulation board commonly blocks window openings. Several inches of insulation are needed to prevent an unusually warm roof, indicative of a grow house, from being spotted by a helicopter infrared device. Extensive insulation and covered exterior openings will hasten flashover conditions. Insulation overhead can mask indications of fire in the attic or in the space between the ceiling of the growing area and the floor above. Marijuana has a distinct, pungent odor, which is readily detectable outside a grow house. To prevent detection, grow house operators use large carbon filters to absorb odors and may seal roof soffit vents when ventilation ductwork terminates in the attic. Odor venting from turbines at or near the roof ridge is less likely to be noticed than odors venting from soffits. Similarly, it is not uncommon to route exhaust ductwork into a toilet to vent the odor of marijuana up a plumbing stack penetrating the roof. Air circulation is vital for growing marijuana and to reduce condensation that can accumulate in cold climates. As a result, growers commonly cut holes in floors to extend ductwork from the basement and between floors; this presents a falling hazard for firefighters as well as a route for vertical fire extension. Firefighters operating in a smoky grow house also risk entanglement in electric wires, water tubing suspended from the ceiling, string to support mature plants, and wire helixes inside flexible ductwork (photo 6).

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(6) Flexible ducts, used to exhaust telltale odor and circulate air, pose a common entanglement hazard in most grow houses. [Photos courtesy of Miami-Dade (FL) Fire Rescue.]

Grow houses commonly have one or more pressurized gas cylinders, which can explode if exposed to fire. The cylinders are used to enrich the concentration of carbon dioxide (CO2) to hasten growth of the plants. This is achieved by releasing CO2 gas from a cylinder or producing it from a natural gas or a propane-fueled CO2 generator. Increasing the level of CO2 can cause an oxygen-deficient atmosphere. Firefighters entering an enclosed growing space must use their self-contained breathing apparatus until the space is ventilated and metered for adequate oxygen concentration. Propane vapor leaking from a cylinder connected to a carbon-monoxide generator inside a grow house in Miami-Dade County, Florida, exploded, resulting in a partial collapse of the structure and the death of one of its occupants (photo 7). Fortunately, the explosion occurred before the firefighters arrived. Booby traps intended to thwart the theft of plants cannot distinguish among a burglar, a police officer, or a firefighter. Booby traps in grow houses may be sophisticated or as simple as boards with protruding nails positioned on the floor inside of doorways.

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(7) This grow house partially collapsed as the result of an explosion caused by propane leaking from a cylinder. The propane fueled a carbon dioxide generator.

Although it is very difficult to identify a grow house from the outside, firefighters conducting a 360° size-up should suspect any unusual hoses or wires entering a building and report their presence to the incident commander (IC). For example, police officers serving a warrant at a suspected grow house by chance happened to notice something unusual about the house next door to the suspected house: Two hoses from the swimming pool pump entered the house through a hole in an exterior wall. The officers suspected that the hoses were connected to a heat pump used to air-condition a grow operation. Their suspicions were raised when they examined the other side of the house and found large-gauge electric wires that evidently tapped into the underground electrical service before it entered the meter (photo 8).

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(8) These wires to a grow house tapped into the underground electrical service before the meter. (Photo by Eric Goodman.)

The first indication of a grow operation observed by firefighters operating in limited visibility may be a garden hose leading to a large garbage can containing water and a submersible pump, commonly used to water marijuana plants. Similarly, pumps, hoses, or plastic containers in a bath tub or shower are also suspect. Window openings covered on the inside are usually concealed by blinds and are impossible to detect; however, firefighters breaking windows from the outside for ventilation who encounter any type of covering on the inside should immediately notify the IC of a suspected grow house.

Remember that grow houses are typically secured extensively to prevent detection and break-ins. Consequently, firefighters entering a suspected grow house should rely on only one means of escape—the door through which they entered; all other doors and windows may be blocked or covered. Accordingly, companies operating on the exterior of a suspected grow house should rapidly force alternate means of egress for firefighters operating inside.

There is a significant civilian life hazard at many grow houses because a portion of a residence is used for growing while the remainder is occupied by families with children. Unfortunately, innocent children are at risk because of their parents’ greed; the front door may be their only means of escape from fire, because all other doorways are blocked and the windows are covered. Firefighters searching for occupants of a suspected grow house should strongly consider vent-enter-search (VES) operations. This tactic involves breaking windows from the outside, completely removing the sash and any covering on the inside, making entry, and searching the area near the window. VES allows rapid entry and search of bedrooms, which can be difficult to locate from the inside because of a grow house’s makeshift partitions.

Firefighters place themselves at great risk when they enter a fire building without knowing its occupancy because they literally do not know what they’re getting into. Knowing a building’s occupancy or use gives firefighters a general idea of its floor plan and what hazards to expect. Firefighters are at greater risk, however, when they enter a house thinking it is a residential occupancy and are not aware that it is used for a marijuana-growing operation. Recognizing a grow house early and being aware of the associated hazards are keys to reducing the risk to firefighters operating at fires in these dangerous and illegal occupancies.

Thanks to Sgt. Chris McManus, Miami-Dade (FL) Police Narcotics Bureau, for his assistance with this article.

BILL GUSTIN, a 37-year veteran of the fire service, is a captain with Miami-Dade (FL) Fire Rescue and lead instructor in his department’s officer training program. He began his fire service career in the Chicago area and teaches fire training programs in Florida and other states. He is a marine firefighting instructor and has taught fire tactics to ship crews and firefighters in Caribbean countries. He also teaches forcible entry tactics to fire departments and SWAT teams of local and federal law enforcement agencies. Gustin is an editorial advisory board member of Fire Engineering.


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