N.Y.C. Admin. Code § MC 510: Section MC 510: Hazardous Exhaust Systems

510.1 General.

This section shall govern the design and construction of duct systems for hazardous exhaust and shall determine where such systems are required. Hazardous exhaust systems are systems designed to capture and control hazardous emissions generated from product handling or processes, and convey those emissions to the outdoors. Hazardous emissions include flammable vapors, gases, fumes, mists or dusts, and volatile or airborne materials posing a health hazard, such as toxic or corrosive materials. For the purposes of this section, the health-hazard rating of materials shall be as specified in NFPA 704.

For the purposes of the provisions of Section 510, a laboratory shall be defined as a building or portion thereof wherein chemicals or gases are used or synthesized on a nonproduction basis for testing, research, experimental, instructional or educational purposes.

510.2 Where required.

A hazardous exhaust system shall be required wherever operations involving the handling or processing of hazardous materials, in the absence of such exhaust systems and under normal operating conditions, have the potential to create one of the following conditions:

1. A flammable vapor, gas, fume, mist or dust is present in concentrations exceeding 25 percent of the lower flammability limit of the substance for the expected room temperature.

2. A vapor, gas, fume, mist or dust with a health-hazard rating of 4 is present in any concentration.

3. A vapor, gas, fume, mist or dust with a health-hazard rating of 1, 2 or 3 is present in concentrations exceeding 1 percent of the median lethal concentration of the substance for acute inhalation toxicity.

Exception: Laboratories, as defined in Section 510.1, except where the concentrations listed in Item 1 are exceeded, or a vapor, gas, fume, mist or dust with a health-hazard rating of 1, 2, 3 or 4 is present in concentrations exceeding 1 percent of the median lethal concentration of the substance for acute inhalation toxicity.

510.2.1 Lumber yards and woodworking facilities.

Equipment or machinery located inside buildings at lumber yards and woodworking facilities that generates or emits combustible dust shall be provided with an approved dust-collection and exhaust system installed in conformance with this section and the New York City Fire Code. Equipment and systems that are used to collect, process or convey combustible dusts shall be provided with an approved explosion-control system.

510.2.2 Combustible fibers.

Equipment or machinery within a building that generates or emits combustible fibers shall be provided with an approved dust-collecting and exhaust system. Such systems shall comply with this code and the New York City Fire Code.

510.3 Design and operation.

The design and operation of the exhaust system shall be such that flammable contaminants are diluted in noncontaminated air to maintain concentrations in the exhaust flow below 25 percent of the contaminant's lower flammability limit.

510.4 Independent system.

Hazardous exhaust systems shall be independent of other types of exhaust systems.

510.5 Incompatible materials and common shafts.

Incompatible materials, as defined in the New York City Fire Code, shall not be exhausted through the same hazardous exhaust system. Hazardous exhaust systems shall not share common shafts with other duct systems, except where such systems are hazardous exhaust systems originating in the same fire area.

Exception: The provision of this section shall not apply to laboratory exhaust systems where all of the following conditions apply:

1. All of the hazardous exhaust ductwork and other laboratory exhaust within both the occupied space and the shafts are under negative pressure while in operation.

2. The hazardous exhaust ductwork manifolded together within the occupied space must originate within the same fire area.

3. Hazardous exhaust ductwork originating in different fire areas and manifolded together in a common shaft shall use steel sub-ducts in accordance with Chapter 6.

4. Each control branch has a flow regulating device.

5. Perchloric acid hoods and connected exhaust shall be prohibited from manifolding.

6. Radioisotope hoods are equipped with filtration, carbon beds, or both where required by the registered design professional.

7. Biological safety cabinets are filtered.

8. Each hazardous exhaust duct system shall be served by redundant exhaust fans that comply with either of the following:

8.1. The fans shall operate simultaneously in parallel and each fan shall be individually capable of providing the required exhaust rate.

8.2. Each of the redundant fans is controlled so as to operate when the other fan has failed or is shut down for servicing.

510.6 Design.

Systems for removal of vapors, gases and smoke shall be designed by the constant velocity or equal friction methods. Systems conveying particulate matter shall be designed employing the constant velocity method.

510.6.1 Balancing.

Systems conveying explosive or radioactive materials shall be prebalanced by duct sizing. Other systems shall be balanced by duct sizing with balancing devices, such as dampers. Dampers provided to balance air flow shall be provided with securely fixed minimum-position blocking devices to prevent restricting flow below the required volume or velocity.

510.6.2 Emission control.

The design of the system shall be such that the emissions are confined to the area in which they are generated by air currents, hoods or enclosures and shall be exhausted by a duct system to a safe location or treated by removing contaminants.

510.6.3 Hoods required.

Hoods or enclosures shall be used where contaminants originate in a limited area of a space. The design of the hood or enclosure shall be such that air currents created by the exhaust systems will capture the contaminants and transport them directly to the exhaust duct.

510.6.4 Contaminant capture and dilution.

The velocity and circulation of air in work areas shall be such that contaminants are captured by an airstream at the area where the emissions are generated and conveyed into a product-conveying duct system. Contaminated air from work areas where hazardous contaminants are generated shall be diluted below the thresholds specified in Section 510.2 with air that does not contain other hazardous contaminants.

510.6.5 Makeup air.

Makeup air shall be provided at a rate approximately equal to the rate that air is exhausted by the hazardous exhaust system. Makeup air intakes shall be located in accordance with Section 401.4.

510.6.6 Clearances.

The minimum clearance between hoods and combustible construction shall be the clearance required by the duct system.

510.6.7 Ducts.

Hazardous exhaust duct systems shall extend directly to the exterior of the building and shall not extend into or through ducts and plenums.

510.7 Penetrations.

Penetrations of structural elements by a hazardous exhaust system shall conform to Sections 510.7.1 through 510.7.4.

Exception: Duct penetrations within Group H-5 occupancies as allowed by the New York City Building Code.

510.7.1 Fire dampers and smoke dampers.

Fire dampers and smoke dampers are prohibited in hazardous exhaust ducts.

510.7.1.1 Shaft penetrations.

Hazardous exhaust ducts that penetrate fire-resistance-rated shafts shall comply with Section 714.3.1 or 714.3.1.2 of the New York City Building Code.

510.7.2 Floors.

Hazardous exhaust systems that penetrate a floor/ceiling assembly shall be enclosed in a fire-resistance-rated shaft constructed in accordance with the New York City Building Code.

510.7.3 Wall assemblies.

Hazardous exhaust duct systems that penetrate fire-resistance-rated wall assemblies shall be enclosed in fire-resistance-rated construction from the point of penetration to the outlet terminal, except where the interior of the duct is equipped with an approved automatic fire suppression system. Ducts shall be enclosed in accordance with the New York City Building Code requirements for shaft construction and such enclosure shall have a minimum fire-resistance rating of not less than the highest fire-resistance-rated wall assembly penetrated.

510.7.4 Fire walls.

Ducts shall not penetrate a fire wall.

510.8 Suppression required.

Ducts shall be protected with an approved automatic fire suppression system installed in accordance with the New York City Building Code.

Exceptions:

1. An approved automatic fire suppression system shall not be required in ducts conveying materials, fumes, mists and vapors that are nonflammable and noncombustible under all conditions and at any concentrations.

2. Automatic fire suppression systems shall not be required in metallic and noncombustible, nonmetallic exhaust ducts in semiconductor fabrication facilities.

3. An approved automatic fire suppression system shall not be required in ducts where the largest cross-sectional diameter of the duct is less than 10 inches (254 mm).

4. For laboratories, as defined in Section 510.1, approved automatic fire suppression systems shall not be required in laboratory hoods or exhaust systems.

510.9 Duct construction.

Ducts used to convey hazardous exhaust shall be constructed of materials approved for installation in such an exhaust system and shall comply with one of the following:

1. Ducts shall be constructed of approved G90 galvanized sheet steel, with a minimum nominal thickness as specified in Table 510.9.

2. Ducts used in systems exhausting nonflammable corrosive fumes or vapors shall be constructed of nonmetallic materials that exhibit a flame spread index of 25 or less and a smoke-developed index of 50 or less when tested in accordance with ASTM E 84 or UL 723 and that are listed and labeled the application.

Where the products being exhausted are detrimental to the duct material, the ducts shall be constructed of alternative materials that are compatible with the exhaust.

Table 510.9 Minimum Duct Thickness

Diameter of Duct or Maximum Side Dimension

Minimum Nominal Thickness

Nonabrasive Materials

Nonabrasive/abrasive Materials

Abrasive Materials

0 - 8 inches

0.028 inch (No. 24 gage)

0.034 inch (No. 22 gage)

0.040 inch (No. 20 gage)

9 - 18 inches

0.034 inch (No. 22 gage)

0.040 inch (No. 20 gage)

0.052 inch (No. 18 gage)

19 - 30 inches

0.040 inch (No. 20 gage)

0.052 inch (No. 18 gage)

0.064 inch (No. 16 gage)

Over 30 inches

0.052 inch (No. 18 gage)

0.064 inch (No. 16 gage)

0.079 inch (No. 14 inch)

For SI: 1 inch = 25.4 mm.

510.9.1 Duct joints.

Ducts shall be made tight with lap joints having a minimum lap of 1 inch (25.4 mm). Joints used in SMACNA/ANSI Round Industrial Duct Construction Standards and SMACNA/ANSI Rectangular Industrial Duct Construction Standards are also acceptable.

510.9.2 Clearance to combustibles.

Ducts shall have a clearance to combustibles in accordance with Table 510.9.2. Exhaust gases having temperatures in excess of 600°F (316°C) shall be exhausted to a chimney in accordance with Section 511.2.

Table 510.9.2 Clearance to Combustibles

Type of Exhaust or Temperature of Exhaust (°F)

Clearance to Combustibles (inches)

Less than 100

1

100 - 600

12

Flammable vapors

6

For SI: 1 inch = 25.4 mm, °C = ((°F) - 32)/1.8.

510.9.3 Explosion relief.

Systems exhausting potentially explosive mixtures shall be protected with an approved explosion relief system or by an approved explosion prevention system designed and installed in accordance with NFPA 69. An explosion relief system shall be designed to minimize the structural and mechanical damage resulting from an explosion or deflagration within the exhaust system. An explosion prevention system shall be designed to prevent an explosion or deflagration from occurring.

510.10 Supports.

Ducts shall be supported at intervals not exceeding 10 feet (3048 mm). Supports shall be constructed of noncombustible material.