Section 6.3 — Ventilation Systems

(1) Except as provided in Sentence (4), all buildings shall be ventilated in accordance with this Section. e1 (2) Except in storage garages and repair garages covered by Article 6.3.1.3., outdoor air shall be supplied to buildings for ventilation purposes in accordance with one of the following Sections of ANSI/ASHRAE 62.1, “Ventilation for Acceptable Indoor Air Quality,” (a) Section 6.2, Ventilation Rate Procedure, excluding the exception stated in Section 6.2.7.1.2 and note H of Table 6.2.2.1, (b) Section 6.3, Indoor Air Quality Procedure, or (c) Section 6.4, Natural Ventilation Procedure, excluding residential occupancies. (3) Except in storage garages and repair garages covered by Article 6.3.1.3., exhaust ventilation shall be provided in accordance with Section 6.5, Exhaust Ventilation, of ANSI/ASHRAE 62.1, “Ventilation for Acceptable Indoor Air Quality,” as a minimum. (4) Self-contained heating-season mechanical ventilation systems serving only one dwelling unit shall comply with Subsection 9.32.3. (5) Live/work units shall be mechanically ventilated in accordance with the requirements of Sentence (1).

(1) Except as permitted by Sentence (2), the ventilation required by Article 6.3.1.1. shall be provided by mechanical ventilation except that it can be provided by natural ventilation or a combination of natural and mechanical ventilation in (a) buildings of other than residential occupancy having an occupant load of not more than one person per 40 m² during normal use, (b) buildings of industrial occupancy where the nature of the process contained in them permits or requires the use of large openings in the building envelope even during the winter, or (c) seasonal buildings not intended to be occupied during the winter. (2) Where climatic conditions permit, buildings containing occupancies other than residential occupancies, may be ventilated by natural ventilation methods in lieu of mechanical ventilation where engineering data demonstrates that such a method will provide the required ventilation for the type of occupancy.

(1) Unconditioned and unoccupied crawl spaces and attic or roof spaces shall be ventilated by natural or mechanical means as required by Part 5. (See Note A-6.3.1.2.(1))

(1) Except as provided in Sentences (4) and (6), an enclosed storage garage for five or more motor vehicles shall have a mechanical ventilation system designed to (a) limit the concentration of carbon monoxide to not more than 100 parts per million parts of air, (b) limit the concentration of nitrogen dioxide to not more than 3 parts per million parts of air, where the majority of the vehicles stored are powered by diesel-fuelled engines, or (c) provide, during operating hours, a continuous supply of outdoor air at a rate of not less than 3.9 L/s for each square metre of floor area (see Article 3.3.1.21.). (See Note A-6.3.1.3.(1)) (See also Sentence 3.3.5.4.(4)) (2) Mechanical ventilation systems provided in accordance with Clause (1)(a) shall be controlled automatically by carbon monoxide monitoring devices, and systems provided in accordance with Clause (1)(b) shall be controlled by nitrogen dioxide or other acceptable monitoring devices. (See Note A-6.3.1.3.(2)) (3) Mechanical ventilation systems provided in accordance with Sentence (1) shall be designed such that the pressure in the storage garage is less than the pressure in adjoining buildings of other occupancy, or in adjacent portions of the same building having a different occupancy. (4) In storage garages subject to the requirements of Sentence (1), where motor vehicles are parked by mechanical means, the ventilation requirements may be reduced by one half. (5) Except as provided in Sentence (6), ticket and attendant booths of storage garages shall be pressurized with a supply of uncontaminated air. (6) The requirements of Sentences (1) to (5) shall not apply to open-air storeys in a storage garage. (7) A repair garage shall have a mechanical ventilation system designed to limit the exposure of workers to, (a) carbon monoxide to below the time weighted average concentration of 25 parts per million for a normal 8 hour workday or 40 hour work week, and (b) nitrogen dioxide from diesel powered vehicles to below 0.72 parts per million for a normal 8 hour workday or 40 hour work week. (8) In a repair garage, when a repair bay is not immediately adjacent to an outside garage door opening, a system capable of providing continuous general ventilation of not less than 700 L/s per internal bay shall be provided. (9) The general ventilation system described in Sentence (8) shall be designed to, (a) operate continuously, or (b) be controlled automatically by carbon monoxide monitoring devices, located so as to provide full protection throughout the repair garage. (10) The general ventilation system described in Sentence (8) is not required when tail pipes of vehicles are directly connected to local mechanical exhaust systems that terminate outdoors.

(1) Heat recovery ventilators with rated capacities of not less than 25 L/s and not more than 200 L/s shall be installed in accordance with Subsection 9.32.3.

(1) Air contaminants of concern within buildings shall (a) be removed insofar as is possible at their points of origin, and (b) not be permitted to accumulate in concentrations greater than those permitted by good engineering practice such as that described in the publications listed in Sentence 6.2.1.1.(1), measured using the methodology described therein. (2) Systems serving spaces that contain sources of contamination and systems serving other occupied parts of the building but located in or running through spaces that contain sources of contamination shall be designed in such a manner as to prevent the spread of such contamination to other occupied parts of the building. (3) Heating, ventilating and air-conditioning systems shall be designed to minimize the growth and spread of bio- contaminants. (4) Mechanical rooms containing refrigeration equipment shall be ventilated in accordance with CSA B52, “Mechanical refrigeration code”.

(1) Except as provided in Article 3.6.3.5., all commercial cooking equipment shall be provided with ventilation systems designed, constructed and installed to conform to NFPA 96, “Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations.”

(1) This Subsection applies to the design, construction and installation of air duct distribution systems serving heating, ventilating and air-conditioning systems other than those in dwelling units covered by Part 9.

(1) HVAC systems that generate condensate or introduce liquid water into the airstream in the ducts shall be equipped with drain pans that are (a) designed in accordance with Section 5.10, Drain Pans, of ANSI/ASHRAE 62.1, “Ventilation for Acceptable Indoor Air Quality,” (b) provided with an outlet that is piped to the outside of the airstream in a location where condensate can be safely disposed of, (c) installed so that water does not stagnate and drains from the pan, and (d) provided with a drain line that is indirectly connected to a drainage system in accordance with Article 7.4.2.1.

(1) All ducts, duct connectors, associated fittings and plenums used in air duct systems shall be constructed of materials as described in Article 3.6.5.1. (2) Ducts that are used in a location where they may be subjected to excessive moisture shall have no appreciable loss of strength when wet and shall be resistant to moisture-induced corrosion. (3) All ductwork and fittings shall be constructed and installed as recommended in SMACNA Manuals and ASHRAE Standards. (4) All duct materials shall be suitable for exposure to the temperature and humidity of the air being carried and shall be resistant to corrosion caused by contaminants in the air being conveyed in the duct.

(1) Air duct systems shall have tight-fitting connections throughout.

(1) Coverings, linings and associated adhesives and insulation used in air ducts, plenums and other parts of air duct systems shall comply with Article 3.6.5.4. (2) Duct linings shall be installed so that they will not interfere with the operation of volume or balancing dampers or of fire dampers, fire stop flaps and other closures.

(1) The clearance of ducts and plenums from combustible materials shall comply with Article 3.6.5.6.

(1) Rectangular panels in plenums and ducts more than 300 mm wide shall be shaped to provide sufficient stiffness. (2) Where the installation of heating supply ducts in walls and floors creates a space between the duct and construction material, the space shall be fire stopped with noncombustible material at each end. (3) Ducts shall be securely supported by metal hangers, straps, lugs or brackets, except that where zero clearance is permitted, wooden brackets may be used. (4) All round duct joints shall be tight-fitting and lapped not less than 25 mm. (5) Rectangular duct connections shall be made with S and drive cleats. (6) Trunk supply ducts shall not be nailed directly to wood members. (7) Branch ducts shall be supported at suitable spacings to maintain alignment and prevent sagging. (8) Ducts in or beneath concrete slabs-on-ground shall be watertight, corrosion-, decay- and mildew-resistant. (9) Where a supply or return duct is not protected by an insulated exterior wall or where the duct is exposed to an unheated space it shall be insulated to prevent condensation.

(1) In a residential occupancy, air from one suite shall not be circulated to any other suite or to a public corridor. (2) Except as permitted by Sentences (3) and 6.3.2.10.(6), air duct systems serving storage garages shall not be directly interconnected with other parts of the building. (3) Exhaust ducts referred to in Sentence 6.3.2.10.(10) are permitted to exhaust through an enclosed storage garage prior to exhausting to the outdoors, provided (a) the storage garage exhaust system runs continuously, (b) the capacity of the storage garage exhaust system is equal to or exceeds the volume of the exhaust entering the garage, and (c) a leakage rate 1 smoke/fire damper rated in accordance with CAN/ULC-S112.1, “Standard for Leakage Rated Dampers for Use in Smoke Control Systems,” is provided near the duct outlet location in the storage garage to prevent air from the storage garage from entering the exhaust ductwork system in the event the building's exhaust fan is shut down. (4) Except for corridors conforming to Sentence 3.3.1.4.(4) or as permitted in Sentences (5) and (6), a public corridor or corridor serving the public shall not be used as a portion of a supply, return or exhaust air system serving adjoining areas, other than as part of a supply air system serving toilet rooms, bathrooms, shower rooms and similar auxiliary spaces opening directly to the public corridor or corridor used by the public. (5) A public corridor may be used as part of an engineered smoke control system. (6) Infiltration due to corridor pressurization is permitted into a residential occupancy from a public corridor.

(1) In ventilating systems that exhaust air to the outdoors, provision shall be made for the admission of a supply of makeup air in sufficient quantity so that the operation of the exhaust system and other exhaust equipment or combustion equipment is not adversely affected. (2) Makeup air facilities required by Sentence (1) shall be interlocked with the exhaust devices they serve so that both operate together. (3) Where makeup air facilities are intended to introduce air directly from the outdoors to occupied parts of the building in winter, they shall incorporate means of tempering that air to maintain the indoor design temperature.

(1) Supply, return and exhaust air openings located less than 2 m above the floor in rooms or spaces in buildings shall be protected by grilles having openings of a size that will not allow the passage of a 15 mm diam sphere. (2) Outdoor air intakes shall be located so that (a) the quality of the air entering the building complies with Sentences 6.2.1.2.(2) and (3), and (b) they are separated a minimum distance from sources of contaminants in accordance with Table 6.3.2.9. (3) Outdoor air intakes shall be installed not less than 0.3 m above roofs, landscape grades or other surfaces, taking into account anticipated snow accumulation levels. (4) Exterior openings for outdoor air intakes and exhaust outlets shall be shielded from the entry of snow and rain and shall be fitted with corrosion-resistant screens of mesh having openings not larger than 15 mm, except where experience has shown that climatic conditions require larger openings to prevent the screen openings from icing over. (5) Screens required in Sentence (4) shall be accessible for maintenance. (6) Combustible grilles, diffusers and other devices covering supply, return, intake and exhaust openings shall comply with Article 3.6.5.7. Table 6.3.2.9. Minimum Distances of Air Intakes from Sources of Contaminants Forming Part of Sentence 6.3.2.9.(2) Minimum Distance of Source of Contaminants Outdoor Air Intake, m Garage entry of a garage for 5 or more motor vehicles, automobile loading area and drive-in queue 4.5 Truck loading area or dock, and bus parking 7.6 Driveway, parking space, lane, road and similar locations that carry a low volume of traffic 1.5 Thoroughfare, arterial road, freeway, highway and similar locations that carry a high volume of traffic 7.6 Garbage storage/pick-up area and dumpsters 4.5 Discharge from evaporative heat rejection systems 7.6 Sanitary vent 3.5 Kitchen exhaust outlet 3.0 Vent for combustion products from solid fuel-burning appliances 3.0

(1) Except as provided in Sentence (2), exhaust ducts of non-mechanical ventilating systems serving separate rooms or spaces shall not be combined. (2) Exhaust ducts of non-mechanical ventilating systems serving similar occupancies may be combined immediately below the point of final delivery to the outdoors, such as at the base of a roof ventilator. (3) Exhaust ducts of ventilating systems shall have provision for the removal of condensation where this may be a problem. (4) Exhaust outlets shall be designed to prevent back draft under wind conditions. (5) Except as permitted in Sentence (6), exhaust systems shall discharge directly to the outdoors. (See Note A- 6.3.2.10.(5) and (6)) (6) Exhaust systems are permitted to exhaust into a storage garage, provided (a) they serve rooms that are accessible only from that storage garage, (b) the exhaust contains no contaminants that would adversely affect the air quality in the storage garage, and (See Note A-6.3.2.10.(6)(b)) (c) they are designed in accordance with Sentence 6.3.2.7.(3). (See Note A-6.3.2.10.(5) and (6)) (7) Exhaust ducts connected to laundry drying equipment shall be, (a) independent of other exhaust ducts, (b) designed and installed so that the entire duct can be cleaned, and (c) constructed of smooth corrosion-resistant material. (See Note A-6.3.2.10.(7) and (8)) (8) Where collective venting of multiple installations of laundry-drying equipment is used, the ventilation system shall (a) be connected to a common exhaust duct that is vented by one central exhaust fan, (b) include an interlock to activate the central exhaust fan when laundry-drying equipment is in use, and (c) be provided with make-up air. (See Note A-6.3.2.10.(7) and (8)) (9) Exhaust ducts or vents connected to laundry-drying equipment shall discharge directly to the outdoors. (10) Except as provided in Sentence (12) and except for self-contained systems serving individual dwelling units, exhaust ducts serving rooms containing water closets, urinals, basins, showers or slop sinks shall be independent of other exhaust ducts. (11) Except as provided in Sentence (12) and except for self-contained systems serving individual dwelling units, exhaust ducts serving rooms containing residential cooking equipment shall be independent of other exhaust ducts. (12) Two or more exhaust systems described in Sentences (10) and (11) may be interconnected or connected with exhaust ducts serving other areas of the building, provided (a) the connections are made at the inlet of an exhaust fan, and all interconnected systems are equipped with suitable back pressure devices to prevent the passage of odours from one system to another when the fan is not in operation, or (b) the exhaust ducts discharge to a shaft that is served by an exhaust fan having a capacity that is equal to or greater than the combined capacity of the exhaust fans discharging to the plenum multiplied by the operation diversity factor, provided that the exhaust fan serving the shaft operates continuously. (See Note A-6.3.2.10.(12)(b)) (13) Where exhaust ducts containing air from conditioned spaces pass through or are adjacent to unconditioned spaces, the ducts shall be constructed to prevent condensation from forming on the inside or outside of the ducts. (14) Except as provided in Sentence (15), exhaust air shall be provided at a rate not less than 24 L/s for each water closet, urinal, shower or slop sink. (15) Except as provided in Sentence 6.3.1.1.(4), exhaust air shall be provided for fixtures in dwelling units in accordance with ANSI/ASHRAE 62.1, “Ventilation for Acceptable Indoor Air Quality.” (16) Except for wash basins (lavatories), sanitary facilities in a food premises shall be mechanically ventilated and shall be capable of exhausting air at the rate of not less than 24 L/s for each sanitary fixture listed in Sentence (17). (17) The mechanical ventilation described in Sentence (16) applies to rooms containing water closets, urinals, basins, showers or slop sinks.

(1) Return-air systems shall comply with Article 3.6.5.8. (2) Where a ceiling space is used as a return-air plenum, the requirements of Article 3.6.4.3. shall apply. (3) A public corridor or exit shall not be used as a return-air plenum. (4) The return-air system shall be designed to handle the entire air supply. (5) The return-air system shall be designed so that the negative pressure from the circulating fan cannot affect the furnace combustion air supply nor draw combustion products from joints or openings in the furnace or flue pipe. (6) Return-air inlets shall not be installed in an enclosed room or crawl space that provides combustion air to a fuel-fired appliance.

(1) Underground ducts shall (a) be constructed and installed to provide interior drainage from and access to all low points, (b) not be connected directly to a sewer, and (c) be installed and constructed of materials recommended by ASHRAE and SMACNA Standards and HRAI Manuals. (2) A clean-out or pump-out connection shall be provided in an underground duct system at every low point of the duct system.

(1) Air filters for air duct systems shall conform to the requirements for Class 2 air filter units as described in CAN/ULC-S111, “Standard Method of Fire Tests for Air Filter Units.” (2) When electrostatic-type filters are used, they shall be installed so as to ensure that the electric circuit is automatically de-energized when filter access doors are opened or, in dwelling units, when the furnace circulation fan is not operating.

r1 (1) Reserved. (2) Where contaminants of concern are present in the outdoor air of the local area of the building site, ventilation required by Sentence 6.3.1.1.(1) shall be provided by a ventilation system designed to include devices that reduce the concentrations of contaminants to those permitted in the ACGIH's “Industrial Ventilation: A Manual of Recommended Practice for Design” prior to the introduction of outdoor air to indoor occupied spaces.

(1) Evaporative heat rejection systems shall (a) incorporate a drift eliminator or other means to minimize the dispersion of entrained water droplets, and (b) have a design discharge velocity that does not exceed the maximum discharge velocity recommended by the manufacturer. (2) Evaporative heat rejection systems shall be designed so that water continuously circulates through all parts of the system that are normally wetted when the system is operating. (3) Evaporative heat rejection systems and their components shall be constructed of corrosion-resistant, non-porous materials that do not promote the proliferation of disease-causing micro-organisms and that are compatible with disinfectants, biocides and other cleaning agents. (4) Evaporative heat rejection systems shall be installed such that (a) no discharge air bypasses the drift eliminator or other means referred to in Clause (1)(a), and (b) the systems are accessible for cleaning, inspection and maintenance. (5) Except as provided in Sentence (6), air discharged from evaporative heat rejection systems shall discharge away from the building, so as to not re-enter it, to a distance not less than (a) 2.15 m above sidewalks and driveways, (b) 7.6 m from outdoor air intakes, (c) 3 m horizontally or vertically from exterior doors and operable windows, and (d) 3 m horizontally or vertically from occupiable outdoor spaces, excluding maintenance spaces. (See Note A-6.3.2.15.(5) and (6)) (6) Air discharged from evaporative heat rejection systems in health care facilities shall discharge away from the building in compliance with CAN/CSA-Z317.2, “Special requirements for heating, ventilation, and air-conditioning (HVAC) systems in health care facilities.” (See Note A-6.3.2.15.(5) and (6)) (7) Air intakes of evaporative heat rejection systems shall incorporate protective measures to minimize the entrainment of vegetation and other organic matter. (8) Make-up water connections shall be equipped with backflow prevention devices that conform to Article 7.6.2.1. (See Note A-6.3.2.15.(8) and (9)) (9) Water treatment systems and equipment for controlling the proliferation of disease-causing micro-organisms shall (a) be provided in accordance with Section 7.6.2. of ASHRAE Guideline 12, “Minimizing the Risk of Legionellosis Associated with Building Water Systems,” and (b) include means for drainage, dilution, cleaning, and application of chemicals for the control of scale, corrosion and biological contamination. (See Note A-6.3.2.15.(8) and (9)) (10) Drains, overflows and blow-downs shall be connected to the building's drainage system in accordance with Clause 7.4.2.1.(1)(d). (11) Evaporative heat rejection systems shall be provided with access openings, service platforms, fixed ladders and fall- restraint connections to allow inspection, maintenance and testing.

(1) Evaporative air coolers, misters, atomizers, air washers and humidifiers shall be designed in accordance with Sections 8 and 9 of ASHRAE Guideline 12, “Minimizing the Risk of Legionellosis Associated with Building Water Systems.” (2) Systems referred to in Sentence (1) shall (a) be designed so that water continuously circulates through all parts of the system that are normally wetted when the system is operating, and (b) incorporate a method of preventing water stagnation within the system itself and the internal plumbing when the system is not operating. (See Note A-6.3.2.16.(2)) (3) All components of systems referred to in Sentence (1), including filters and evaporation media, shall be constructed of corrosion-resistant, non-porous materials that do not promote the proliferation of disease-causing micro-organisms. (4) Associated sumps shall (a) be constructed of corrosion-resistant, non-porous materials that do not promote the proliferation of disease-causing micro-organisms, (b) include auxiliary drains to prevent the overflow of water into ductwork, and (c) be installed so that they can be flushed, drained, cleaned and disinfected. (5) Where misters, atomizers or air washers are used in ductwork, the affected duct section shall be (a) designed to ensure drainage of unevaporated and accumulated water, and (b) constructed of corrosion-resistant, non-porous materials that do not promote the proliferation of disease-causing micro-organisms. (6) Make-up water connections shall be equipped with backflow prevention devices that conform to Article 7.6.2.1. (See Note A-6.3.2.16.(6))

(1) Fans for heating, ventilating and air-conditioning systems shall be located and installed so that their operation (a) does not adversely affect the draft required for proper operation of fuel-fired appliances, and (b) does not allow the air in the duct system to be contaminated by air or gases from the boiler room or furnace room. (2) Fans and associated air-handling equipment, such as air washers, filters and heating and cooling units, when installed on the roof or elsewhere outside the building, shall be of a type designed for outdoor use.

(1) Vibration isolation connectors in air duct systems shall comply with Article 3.6.5.2.

(1) Tape used for sealing joints in air ducts, plenums and other parts of air duct systems shall comply with Article 3.6.5.3.

(1) Except as provided in Articles 6.3.3.2. and 6.3.3.3., the products of combustion from oil-, gas and solid-fuel-burning appliances shall be vented in conformance with the requirements in the applicable appliance installation standard listed in Article 6.2.1.5. (2) Except as provided in Article 6.2.1.5., vented products of combustion, other than those referred to in Sentence (1), shall be discharged away from the building, so as not to re-enter it, to a distance not less than (a) 2.15 m above sidewalks and driveways, (b) 3 m from outdoor air intakes, (c) 3 m horizontally or vertically from doors and operable windows, and (d) 3 m horizontally or vertically from occupiable outdoor spaces, excluding maintenance spaces. (See Note A-6.3.3.1.(2))

(1) Rectangular masonry or concrete chimneys not more than 12 m in height shall conform to Part 9 if they serve (a) appliances with a combined total rated heat output of 120 kW or less, or (b) fireplaces. (2) Masonry or concrete chimneys other than those described in Sentence (1) shall be designed and installed in conformance with the appropriate requirements in NFPA 211, “Standard for Chimneys, Fireplaces, Vents and Solid Fuel- Burning Appliances.”

(1) Single wall metal smoke stacks shall be designed and installed in conformance with NFPA 211, “Standard for Chimneys, Fireplaces, Vents and Solid Fuel-Burning Appliances.”

(1) Access ladders for chimneys, when provided, shall consist of steel or bronze rungs, built into the walls of the chimneys. (2) Rungs for external ladders shall begin at not less than 2.5 m from ground level.

(1) This Subsection applies to laboratories where dangerous goods, including flammable liquids and combustible liquids, are used in normal laboratory operations in quantities or in a manner that creates a fire or explosion hazard.

(1) A laboratory shall be provided with continuous mechanical ventilation designed to ensure that dangerous goods vapours and particles (a) do not accumulate in the laboratory, (b) are prevented from migrating to other parts of the building, (c) do not accumulate in the ventilation system, (d) are exhausted to the outdoors, and (e) are not returned to the building. (2) A ventilation system required by this Subsection shall be provided with monitoring devices to (a) indicate that the ventilation system is in operation, and (b) sound an alarm if the ventilation system is malfunctioning. (3) A ventilation system required by this Subsection shall be maintained in conformance with Section 4.12. of the Fire Code made under the Fire Protection and Prevention Act, 1997. 6.3.4.2.A. Power-Ventilated Enclosure (1) A power-ventilated enclosure required by the Fire Code made under the Fire Protection and Prevention Act, 1997 shall be designed and constructed to conform to Articles 6.3.4.3. and 6.2.4.4.

(1) The ventilation system for a power-ventilated enclosure referred to in Article 6.3.4.2A. shall (a) conform to NFPA 91, “Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Particulate Solids,” (b) provide continuous exhaust ventilation at an air velocity sufficient to prevent the accumulation of combustible or reactive deposits in the power-ventilated enclosure and its exhaust duct system, (c) confine dangerous goods vapours and particles to the area where they are generated and exhaust them to the outdoors, (d) not return the exhausted air to the building, and (e) be provided with well identified control switches that are (i) located outside the power-ventilated enclosure, and (ii) readily accessible in case of an emergency.

(1) The power-ventilated enclosure referred to in Article 6.3.4.2A. and its exhaust duct system shall (a) except as provided in Sentences (2) and (3), be constructed of noncombustible materials compatible with and chemically resistant to the dangerous goods vapours and particles being exhausted, and (b) be provided with access doors to permit inspection and maintenance of the fan assembly and exhaust ducts. (2) Combustible materials are permitted in the power-ventilated enclosure described in Sentence (1) and its exhaust duct systems if (a) such materials are required by the corrosive or reactive properties of the dangerous goods being used, and (b) their flame-spread rating is not more than 25. (3) The flame-spread rating required by Sentence (2) is permitted to be greater than 25 if an automatic fire suppression system is provided inside the power-ventilated enclosure and its exhaust duct system.