A typical kitchen ventilation system includes an exhaust hood or canopy, ductwork, fan system, and a means of providing adequate make-up air. The entire system must constitute a fire-safe assembly within the building.
Exhaust hoods and canopies capture heat and contaminates in the air by means of filters, extraction baffles (cartridges), and water mist systems. There are many style variations of hoods with canopy styles-a large box with and open bottom-being the most common. Styles selection is based on the type of oven and the expected contaminates to be removed. Referring to FIG. 1, there is a drawing of one type of venting arrangement comprising a back shelf hood over a cook line. While there are several styles of hoods, all fall within two major categories:
Type I hoods carry a listing label and are manufactured and installed according to the manufacturer's and listing agencies' requirements. They are designed to handle grease and include a number of integrated components within the hood.
Type II hoods are used in the collection of steam, vapor, heat, and odors—but not grease. The two sub-classifications of Type II hoods are condensate and heat/fume.
Referring to FIG. 2, there is shown one example of an exhaust hood and associated duct work installed in a ceiling. The exhaust ductwork transfers contaminated air, cooking heat, and grease vapors from the hood to the exhaust fan. Exhaust ducting should have the following qualities:
Ducts that accumulate combustible grease should be constructed from 16-steel or 18-gage stainless steel as per code requirements.
Ducts must be securely supported by non-combustible duct bracing and supports designed to carry the gravity and seismic loads as per code requirements. No fasteners should penetrate the duct.
Duct enclosures made from materials such as of gypsum board, plaster, concrete, or ceramic tiles must be approved as a continuous fire-rated enclosure.
Referring to FIG. 3 there is shown a typical exhaust fan used for a commercial kitchen. Exhaust fans move the heat and contaminated air out of the building. All exhaust fan components must be accessible or have removable access panels for cleaning and inspection and must be designed to contain and drain any excess grease. There are three major types of exhaust fans:
Up-blast fans are typically aluminum centrifugal fans that are designed for roof mounting directly on top of the exhaust stack.
Utility fans are normally roof-mounted with the inlet and outlet 90 degrees from each other and are typically used where high-static pressure losses exist.
Inline fans are typically located in the interior duct and are used where exterior fan mounting is impractical.
Fire Code Requirements
As kitchen ventilation is used, grease laden vapors are carried through the entire system. This action deposits oil on all interior parts of the system which must be cleaned to reduce the risk of fire. The minimum frequency and standard for cleaning is provided by the National Fire Protection Association (NFPA) and fire codes NFPA96.
Cleaning ducting and fans also requires following these codes:
Restaurant NFPA Fire Code 96: 4.1.5
The responsibility for inspection, maintenance, and cleanliness of the ventilation control and fire protection of the commercial cooking operations shall be the ultimate responsibility of the owner of the system provided that this responsibility has not been transferred in written form to a management company or other party.
Fan Access Panel NFPA Fire Code 96: 8.1.5.3.1
Up-blast fans shall be supplied with an access opening of a minimum 76 mm by 127 mm (3 in. by 5 in.) or a circular diameter of 101 mm (4 in.) on the curvature of the outer fan housing to allow for cleaning and inspection of the fan blades.
Electrical Wiring/Fan Hinge NFPA Fire Code 96: 7.8.2.1
Rooftop terminations shall be arranged with or provided with the following: (8) a hinged up-blast fan supplied with flexible weatherproof electrical cable and service hold-open retainer to permit inspection and cleaning that is listed for commercial cooking equipment.
NFPA Fire Code 96: 8.1.1.1
Approved up-blast fans with motors surrounded by the airstream shall be hinged, supplied with flexible weatherproof electrical cable and service hold-open retainers, and listed for this use.
NFPA Fire Code 96: 9.2.1
Wiring systems of any type shall not be installed in ducts.
Rooftop Grease Containment NFPA Fire Code 96: 7.8.2.1
Rooftop termination 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, rainproof, and structurally sound for the service to which it is applied and that will not sustain combustion. (5) A grease collection device that is applied to exhaust systems that does not inhibit the performance of any fan.
NFPA Fire Code 96: 8.1.1.3
Up-blast fans shall have a drain directed to a readily accessible and visible grease receptacle not to exceed 3.8 L (1 gal).
Inspection & Cleaning Frequency NFPA Fire Code 96: 11.4, 11.6.1, 11.6.2
The entire exhaust system shall be inspected for grease buildup by a properly trained, qualified, and certified company or person(s) acceptable to the authority having jurisdiction and in accordance with Table 11.4. [See FIG. 4]. Upon inspection, if the exhaust system is found to be contaminated with deposits from grease-laden vapors, the contaminated portions of the exhaust system shall be cleaned by a properly trained, qualified, and certified company or person(s) acceptable to the authority having jurisdiction. Hoods, grease removal devices, fans, ducts, and other appurtenances shall be cleaned to remove combustible contaminants prior to surfaces becoming heavily contaminated with grease or oily sludge.
Kitchen Ventilation Cleaning Process
The kitchen Ventilation cleaning process can be broken into 5 stages:
Cleaning of Filters
Bagging the Hood
Exhaust fan cleaning
Fans Grease receptacle
Ducting and Hood
Cleaning of Filters
The kitchen exhaust cleaning personnel first remove and clean the filters from the hood, this cleaning is usually done by means of applying a degreaser and washing with high pressure steam over a containment tank to capture all waste generated. This process is complete once all built up oil and grease in no longer present on the visible surfaces.
Bagging the Hood
Once the hoods filters are removed, the cleaning personnel begin what is called the bagging process. Using plastic, tape and clamps, the kitchen hood is surrounded with plastic in a manner to capture all wash water. This is then to be collected and funneled into a collection container and not to fall on the floor or ground.
Exhaust Fan Cleaning
Once the hood is bagged, the cleaning personnel begin the cleaning process of the exhaust fan on the roof. This includes spraying chemical degreasers and high pressure steam onto the interior parts of the fan. During this process all wash water injected into and onto the fans parts is expelled through the precipitation drain and onto the roof and eventually into the storm drain connecting to the roof top. This cleaning process merely displaces the grease from the fan to the roof drain and causes pollution. This task is complete once all built up of oil and grease in no longer present on the visible surfaces.
Fans Grease Receptacle
The grease receptacle must be emptied of oil and grease and or the filters must be changed. Typically this unit is mounted to the fan to collect the oil that drips from the fan during operation. Rain water must also pass this system so grease is easily carried away and onto the roof. A typical capturing design is a collection box that fails its intended function. This is because once full of rain water, the oil floats to the top and spills onto the roof. This grease receptacle can also contain filter media to hold onto the grease and prevent escape; unfortunately this media most often does not get changed due to its unavailability or its inability to perform its deigned function. The result is the hazardous condition depicted in the photograph in FIG. 5.
Ducting and Hood
Once the fan is cleaned, chemical degreasers and high pressure steam are sprayed into the ducting below the fan leading down from the roof and towards the kitchen below. In most cases access doors can be found that supply additional cleaning points for further cleaning. This wash water and chemical flows towards the hood and is then directed by the tarp into the collection container. Once the ducting is cleaned the hood is washed by the same manor of steam and chemicals. All waste water is then disposed of according to the local sewer use bylaw.
The Exhaust Fan Drain Spout
Referring back to FIG. 3, there is shown one example of an exhaust fan. Since the first edition of NFPA96 in 1961 exhaust fan design has improved in order to meet rigid fire safety requirements. Thanks to the adoption of these codes by local fire departments across North America there have been dramatic improvements in fire safety. Prior to the enforcement of these codes, fans would discharge oil directly and uncontrollably from multiple drain points directly onto the roof. As restaurants upgraded over the years to conform to the NFPA standards, exhaust fans have become more reliable and waste discharge points have been focused to one spout.
Through this spout, rainwater that falls into the interior of the fan is permitted to escape.
Without the spout, water would build up inside the fan and eventually spill into the interior of the building.
This spout also permits excess oil to be released from the fan
Exhaust Fan Grease Discharge
Still referring to FIG. 3, exhaust fans are welded to their base; these fans rarely leak or drain from any place other than the spouts. However, exhaust fans have a silicon seal around the bottom and these seals typically begin to leak within one year of installation. The only way to properly reseal these leaks is by an adhesive. Silicon will break down under oily conditions.
Another common problem with a silicon seal is that the exhaust fan cleaning process tends to remove any silicon and makes replacement necessary. An adhesive will withstand both the properties of operating and cleaning.
Environmental Requirements
The kitchen exhaust fan has proven to be the most difficult to manage both during operation and maintenance. Oil can be observed leaking from the fan during the cooking operation and rain provides the transportation it needs to be carried to the roof and drain. This event is both harmful for the roof and the environment.
When servicing the exhaust fan, a typical service company will use high pressure steam, water and chemicals. These methods are used to break down the oil and grease from exhaust fan.
Grease and chemicals can be observed discharging from the drain spout during the cleaning process. Costly truck mounted vacuums or effective onsite improvisation is needed to avoid this infraction.
Therefore, considering the above shortcomings, there is still a requirement for a device that will capture contaminated water waste and grease operation and maintenance and eliminate the pollution caused by cleaning and operation of exhaust fans. There is also a requirement for a device that will help restaurants and cleaning personnel to meet stringent fire codes and anti-pollution codes.