Equipment to manage fumigation, CO2 enrichment, high intensity lighting, large volume humidity control, and oil extraction are commonplace in industrial facilities and are becoming increasingly common in burgeoning marijuana grow and processing facilities.

The legalization of marijuana in Washington, Colorado, and other states has created a market for the growth of marijuana that has seen its share of fires, explosions, code violations and other mishaps as amateur growers and entrepreneurs attempt to transition into large commercial facilities operators.

In this article, mechanical engineer, Bruce Straughan, P.E. covers some of the equipment and processes that are present in marijuana grow and processing facilities and discusses the potential consequences that can arise if they are not managed in a professional manner.

Marijuana Facilities

Due to changes in the laws of certain states in the last several years, there has been a dramatic increase in the number of facilities used in the United States for the cultivation, processing, and retail selling of marijuana. This article provides an overview of the equipment typically installed in these facilities, their operation, and applicable building codes and standards.

The Legal Landscape

As of early 2016, four states have passed laws legalizing marijuana for recreational use, and a total of twenty-three states have legalized it for medical use. Although these laws provide for the cultivation, processing, and retail selling of marijuana to be regulated at the state level, these activities remain illegal under federal law. The U.S. Department of Justice has stated its policy on drug enforcement priorities, and they include preventing revenue from the sale of marijuana from going to criminal enterprises, preventing the diversion of marijuana from states where it is legal under state law to other states, and preventing state-authorized marijuana activity from being used as a cover for other illegal drugs or illegal activity. Outside of its stated enforcement priorities, however, the federal government has traditionally relied on state and local authorities to address marijuana activity through enforcement of their own laws. Although, some federal drug raids of facilities that were legal under state law have occurred, they have been rare. And the marijuana industry has continued to flourish. According to a report in the New York Times, legal sales of marijuana in the U.S. are forecast to reach $6.7 billion in 2016.

The Anatomy of a Grow Facility

In decades past, marijuana was grown mainly outdoors. Indoor grow rooms utilizing high intensity lamps offer many advantages to the grower, including better security, protection from bad weather, protection from outdoor contaminants and pests, and the ability to control the environment to ideal temperature, humidity, and air quality conditions. This control ability allows for greatly increased crop yields.

Commercial grow facilities will typically contain the following systems and equipment:

  • High intensity lamps
  • Heating, air conditioning, and humidity control equipment
  • Ventilation fans
  • Fans to circulate air around the room
  • CO2 emitting equipment
  • Irrigation system
  • Chemicals for fertilizer and pesticides
  • Fire protection system
  • Security systems
  • Computerized control system to monitor the environment and operate the equipment to maintain optimum conditions to maximize the crop yield.

Codes and Standards – Managing the Hazards

Building permits and inspections by local building officials are required for all legal commercial marijuana operations regardless of whether the facility is a new building project or a remodel to an existing building. As long as marijuana facilities are designed, constructed, and operated according to applicable codes and standards, the risk of harm to people inside the facility and the surrounding areas is greatly mitigated. But the various systems in a facility do warrant consideration of any potential hazards, and proper installation and operating procedures must be carefully followed. An improperly designed, constructed and operated facility can also cause damage to the property or the product.


Without natural light, grow rooms depend on grow lights which need to replicate the parts of the sunlight spectrum that the marijuana plants need at each stage of growth. High-pressure sodium lamps are a type of high intensity lamp that has become popular for grow rooms, and 1000 watt bulbs are often selected. These lamps have a high electrical demand and emit a great deal of heat. If these lamps are located too close to combustible materials, fires can occur. Grow lights may be turned off at night and the duration of the lights out period can be gradually altered to simulate the changing seasons and trigger plants to enter the flowering stage.

CO2 Enrichment

The rate of photosynthesis of plants is greatly affected by the concentration of CO2 in the air in the room. CO2 enrichment systems are typically in the form of a compressed CO2 gas cylinder or a natural gas burner that emits products of combustion into the room. Under normal operation, room CO2 is maintained at an elevated level (1500 ppm) but well below hazardous levels and with safety controls, alarms, and warning signs. Either system type presents potential asphyxiation hazards if not properly controlled. The fuel-fired type also presents a CO hazard and is regulated by the International Mechanical Code (IMC) as a non-vented fuel-fired appliance, requiring a CO detector interlocked with an exhaust fan.


Fumigation is regulated by fire codes and typically requires an operational permit. The methods of most concern are sulfur burners used to control mildew and CO2 fumigation to control pests. Sulfur burners heat sulfur, creating sulfur dioxide. If inhaled, sulfur dioxide contacts moisture in the lungs, creating sulfuric acid and can burn the respiratory tract. CO2 can be used to fumigate at levels above OSHA’s immediately dangerous to life or health level of 40,000 ppm to control pests. Both of these operations are of concern to workers entering the space, adjacent tenants unaware of this fumigation activity, or first responders entering in the event of a fire.


Ventilation systems are important for removing contaminants from the space and also help with keeping the space cool. Marijuana plants emit a very strong “skunk like” odor, and local authorities typically require ventilation systems to be installed such that any odors are prevented from leaving the premises. This is usually accomplished by installing a charcoal filter on the discharge of the exhaust duct. Other methods to reduce odors include ozone generators and ionizers.

Heating, Air Conditioning, and Humidity Control

Due to the high heat output of the grow lamps, indoor grow facilities require air conditioning. Marijuana plants grow best at temperatures in the range of 68 to 72 degrees F, and heating equipment is also needed to maintain this optimal temperature range. The optimum humidity range is about 50% to 60% relative humidity. Growing plants transpire a significant amount of water vapor and will cause the air in the room to become very humid if not controlled. During times when the grow lights are on, the dehumidifying effect of the air conditioning unit will typically keep the humidity levels within an acceptable range. When the lights are off, however, a separate dehumidification unit or a reheat coil in the air conditioning system are typically needed. In order to maximize the rate of plant growth, humidity levels must be kept in the optimum range. If the humidity gets excessively high, the grow room becomes a conducive environment for the growth of mold and pathogenic organisms. The walls and ceiling construction of the room should include vapor barriers and corrosion resistant materials. The walls should have sufficient insulation behind the vapor barrier to minimize the chances of moisture in the air condensing and forming water droplets on the wall.

Fire Protection

Grow facilities are classified under the International Building Code (IBC) as an F-1 Occupancy, Factory Industrial, Moderate Hazard. If the floor area of the facility exceeds 12,000 sq. ft., then a fire sprinkler system is required. IBC also requires fire walls with a one-hour separation between the facility and any adjacent occupancy as well as wall and ceiling finishes with a flame spread index within the limits specified in the code. Means of Egress as required in IBC, Chapter 10 is an important consideration for the facility. Marijuana growers typically do not grow in a building with one large open room. They need to isolate the plants that are at different stages of growth. Large converted warehouses can be maze-like with multiple rooms. Care must be taken to ensure that egress paths are clear and do not become blocked by equipment or storage containers.


Grow rooms should be provided with floor drains to remove spilled water and nutrient solutions. The drains should be trapped and equipped with screens to catch any plant material or other debris. The International Plumbing Code requires that water supply lines used for irrigation purposes be provided with back-flow preventers to protect the domestic water supply from contamination.


Grow facilities have a very high electrical demand due to the grow lights, air conditioning units, and other equipment. The electrical system must be sized and installed in accordance with the National Electric Code (NEC). Fire Codes prohibit the use of extension cords or power strips as permanent wiring to equipment, lighting, fans, etc. Overloaded electrical wiring has caused fires in some marijuana grow facilities. In addition to ensuring that the electrical system inside the building is designed and installed properly, the electric service entrance equipment and conductors for the building need to be evaluated. If the facility was created as a remodel to an existing building, it may be necessary for the electric utility company to upgrade the conductors and/or transformer serving the building.


Because the sale of marijuana is not legal under federal law, facility operators have found it difficult or impossible to obtain banking services and operate as all-cash businesses. Between marijuana inventory and cash on hand, security is a big concern for any marijuana facility, especially retail centers. Local codes can vary, but in some states, an alarm system and video surveillance system are required by law.

Processing Facilities for Marijuana Infused Products

Manufacture of marijuana infused products is becoming more prevalent as the industry seeks a more concentrated form of THC, the main psychoactive chemical of marijuana plants. It can be extracted from plant leaves and buds in the form of highly concentrated oil extracts, commonly known as “hash oil.” The extract oil is used in edible goods, or the oil can be smoked or used in vapor cigarettes. There are many ways to extract the oil, most of which use hazardous materials. Any legal extraction operation will draw close scrutiny from local building and fire code officials who will typically review the extraction process and issue a marijuana extraction operational permit to ensure it is performed in compliance with the applicable codes.

Extraction using butane as a solvent is the most cost effective yet the most dangerous method used. Fire codes prohibit open releases of butane to the atmosphere during the extraction process. Several manufacturers produce equipment that cycles butane around a closed-loop system passing the butane through the plant material. The butane under pressure in liquid form acts as a solvent and removes the THC from the plant. The butane is then recollected, and the extract oil can then be retrieved. Denver, Colorado was the first U.S. city to begin regulating the butane hash oil process as a commercial operation, and requires an engineering analysis, signed and sealed by a licensed professional engineer to be submitted for approval. The basis of the analysis is National Fire

Protection Association (NFPA) 58, Liquefied Petroleum Gas Code. Businesses using this equipment are required to have a hazardous material exhaust system installed to capture any potential release of butane, and a hydrocarbon detector to alert the operator of butane leaks. The exhaust fan is required to be connected to an emergency power system per NFPA 70. Depending on the quantity of butane used, the facility may be classified under IBC as a Group H, High Hazard Occupancy. Requiring closed systems and an equipment-approval process is critical to ensure the extraction process is done safely. In 2014, there were 32 reported butane hash-oil explosions in Colorado alone, caused by using unapproved butane open-blast extraction methods. This method releases butane to the atmosphere with the user standing in a cloud of flammable gas. Because this open system type extraction can be performed so cheaply, it is used in both commercial and residential settings.

CO2 extraction is another method of producing hash oil from marijuana. In Denver, the equipment must follow the same approval and permitting process as the butane equipment. Although there is no chemical explosion risk like there is with butane, the systems can run at pressures as high as 10,000 pounds per square inch (psi). Consequently, the equipment must be reviewed to ensure it is constructed properly. Businesses using this equipment are required to perform the extraction in a dedicated room, and a local CO2 alarm is required to alert of CO2 leaks.

Another extraction method is an alcohol distillation or heated evaporation process. Although alcohol is the most common, almost any flammable liquid can be used. Marijuana is soaked in alcohol and then the liquid is boiled off, leaving the oil behind. This type of process is required to comply with NFPA 30. Larger operations recapture the alcohol in a distillation process for reuse. A hazardous exhaust hood is required over the extraction process to capture any flammable vapors released. Equipment must be rated for heating flammable liquids, and open flames are prohibited.

Residential Facilities Pose Many Concerns

In 2015, a law went into effect in Colorado that prohibits the use of butane in residential buildings for extracting oil from marijuana plants. It is legal to cultivate plants inside residential buildings within certain limits as stated by law in some states. Oftentimes, lighting and equipment used in residential operations is not installed or operated according to code, and many concerns have arisen.

Electrical work is not always done with a building permit or done by licensed contractors. Unsafe electrical practices are common, including open wiring, inadequate fuses or circuit breakers, bad connections, and overloading of circuits, dramatically increasing the likelihood of fires and explosions. High intensity grow lamps can reach a surface temperature of 500 degrees F or higher and also pose a fire hazard.

Home based growers have been known to vent the exhaust from gas-fired appliances such as water heaters or furnaces directly into their grow rooms to provide CO2 enrichment. This is a blatant violation of mechanical codes and poses a risk of carbon monoxide poisoning.

The warm, humid environment ideal for plant growth is also conducive for the growth of mold. Since residential operations typically lack the robust humidity controls found in commercial operations, the likelihood of excessively high humidity levels is greatly increased. This can lead to property and product damage from mold on the walls and the structure and to the growth of pathogenic organisms on the product.

Crime related to residential operations is also a concern, with home invasions to steal crops, equipment, and cash known to occur. Laws typically limit the number of plants that can be cultivated by a single person to a small number. But the limit for a single house can be greatly increased by obtaining a doctor’s recommendation for medical marijuana and by multiple adults living in the same house.

Know your Code

It is important to remember that marijuana processing and manufacturing in all areas is covered by Fire and Safety Code. Some cities and areas allow home-based grows, but the regulated industry is moving away from these into more controlled conditions. A “regulated” industry means just that: regulations. It is important to keep abreast of the law and safety code in your state or local area, rather than be caught unaware (and cited for violations), or have your license suspended or revoked.

(FEATURED EXPERT: Bruce Straughan, P.E., CEM  Mechanical Engineer & Building Systems Expert. This article was originally published by For more details, please see the following link: