Fan Smoke Detector Requirements
2003-01-28 | Stan Fuhrhop
The concept for fan smoke detection is to have a detector located downstream of the fan discharge but before any branch duct take-offs.
One needs to be wary of having the detector too close and too low at the discharge of a centrifugal fan with a scroll housing. The loading of air to the top as it comes off the wheel could setup some turbulence flow that fails to allow the detector to operate properly.
The IMC expands on the NFPA/UMC requirement to include detection at floor take-offs of return air on multi-story buildings and those spaces comprised of multiple small air handling equipment having individual air flows less than 2,000 cfm in which the cumulative air flow over exceeds 2,000 cfm. The latter of which includes fan coil units, fan terminal units and cooling-only terminal units. Local amendments aside, such as Denver, the IMC is the most restrictive of the three codes types listed here.
Exception is allowed when the building is provided with a smoke detection system that can signal the equipment to shut down. It may be necessary to indicate the shutdown requirements and provisions on the mechanical drawings to eliminate FUD (fear, uncertainty and doubt).
Click on the links below to jump to the appropriate section:
NFPA 90A - 1999 UMC 1997 UMC 2000 IMC 2000

NFPA 90A-1999

*4-4 Smoke Detection for Automatic Control.

4-4.1 Testing.

All automatic shutdown devices shall be tested at least annually.

*4-4.2 Location.

Smoke detectors listed for use in air distribution systems shall be located as follows:

  1. Downstream of the air filters and ahead of any branch connections in air supply systems having a capacity greater than 2000 ft3/min (944 L/sec).
  2. At each story prior to the connection to a common return and prior to any recirculation or fresh air inlet connection in air return systems having a capacity greater than 15,000 ft3/min (7080 L/sec) and serving more than one story.

Exception No. 1: Return system smoke detectors shall not be required where the entire space served by the air distribution system is protected by a system of area smoke detectors.

Exception No. 2: Fan units whose sole function is to remove air from the inside of the building to the outside of the building.

 

*Appendix Explanations

A-4-4

The use of smoke detectors in relationship to HVAC systems and high air movement areas and the details regarding their optimum installation are covered in NFPA 72, National Fire Alarm Code, 5-3.6.6.

Protection provided by the installation of smoke detectors and related requirements is intended to prevent the distribution of smoke through the supply air duct system and, preferably, to exhaust a significant quantity of smoke to the outside. Neither function, however, guarantees either the early detection of fire or the detection of smoke concentrations prior to dangerous smoke conditions where smoke movement is other than through the supply air system.

Where smoke-control protection for a facility is determined to be needed, see NFPA 92A, Recommended Practice for Smoke-Control Systems.

A-4-4.2

The summation of the capacities of individual supply-air fans should be made where such fans are connected to a common supply air duct system (i.e., all fans connected to a common air duct supply system should be considered as constituting a single system with respect to the applicability of the Chapter 4 provisions that are dependent on system capacity).

 

UMC 1997

M608 - SHUTOFF FOR SMOKE CONTROL

Air-moving systems supplying air in excess of 2,000 cubic feet per minute (940 L/s) to enclosed spaces within buildings shall be equipped with an automatic shutoff. Automatic shutoff shall be accomplished by interrupting the power source of the air-moving equipment upon detection of smoke in the main supply-air duct served by such equipment. Smoke detectors shall be labeled by an approved agency for air-duct installation and shall be installed in accordance with the manufacturer's installation instructions. Such devices shall be compatible with the operating velocities, pressures, temperatures and humidities of the system. Where fire detection or alarm systems are provided for the building, the smoke detectors required by this section shall be supervised by such systems.

EXCEPTIONS:

1. When the space supplied by the air-moving equipment is served by a total coverage smoke-detection system complying with UFC Standard 10-2, interconnection to such system may be used to accomplish the required shutoff.

2. Automatic shutoff is not required when all occupied rooms served by the air-handling equipment have direct exit to the exterior and the travel distance does not exceed 100 feet (30.4 m).

3. Automatic shutoff is not required for Group R, Division 3 and Group U Occupancies.

4. Automatic shutoff is not required for approved smoke-control systems or where analysis demonstrates shutoff would create a greater hazard, such as may be encountered in air-moving equipment supply specialized portions of Group H Occupancies. Such equipment shall be required to have smoke detection with remote indication and manual shutoff capability at an approved location.

 

UMC 2000 (there are slight differences from 1997 underlined)

M609 - Automatic Shutoff

Air-moving systems supplying air in excess of 2,000 cubic feet per minute (940 L/s) to enclosed spaces within buildings shall be equipped with an automatic shutoff. Automatic shutoff shall be accomplished by interrupting the power source of the air-moving equipment upon detection of smoke in the main supply-air duct served by such equipment. Smoke detectors shall be labeled by an approved agency for air-duct installation and shall be installed in accordance with the manufacturer's approved instructions. Such devices shall be compatible with the operating velocities, pressures, temperatures and humidities of the system. Where fire detection or alarm systems are provided for the building, the smoke detectors required by this section shall be supervised by such systems.

EXCEPTIONS:

1. When the space supplied by the air-moving equipment is served by a total coverage smoke-detection system complying with the Fire Code, interconnection to such system may be used to accomplish the required shutoff.

2. Automatic shutoff is not required when all occupied rooms served by the air-handling equipment have direct exit to the exterior and the travel distance does not exceed 100 feet (30480 mm).

3. Automatic shutoff is not required for Group R, Division 3 and Group U Occupancies.

4. Automatic shutoff is not required for approved smoke-control systems or where analysis demonstrates shutoff would create a greater hazard, such as may be encountered in air-moving equipment supply specialized portions of Group H Occupancies. Such equipment shall be required to have smoke detection with remote indication and manual shutoff capability at an approved location.

 

IMC 2000

M606

SMOKE DETECTION SYSTEMS CONTROL

M606.1 Controls required. Air distribution systems shall be equipped with smoke detectors listed and labeled for installation in air distribution systems, as required by this section.

M606.2 Where required. Smoke detectors shall be installed where indicated in M606.2.1 through M606.2.3.

EXCEPTION: Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.

M606.2.1 Return air systems. Smoke detectors shall be installed in return air systems with a design capacity greater than 2,000 cfm (0.9 m^3/s), in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.

EXCEPTION: Smoke detectors are not required in the return air system where the space served by the air distribution system is protected by a system of area smoke detectors in accordance with the International Building Code. The area smoke detector system shall comply with M606.4.

M606.2.2 Common supply and return air systems. Where multiple air-handling systems share common supply or return air ducts or plenums with a combined design capacity greater than 2,000 cfm (0.9 m^3/s), the return air system shall be provided with smoke detectors in accordance with M606.2.1.

EXCEPTION: Individual smoke detectors shall not be required for each variable air volume (VAV) zone unit or VAV-type fan-powered terminal unit, provided that such units do not have an individual design capacity greater than 2,000 cfm (0.9 m^3/s) and will be shut down by activation of one of the following:

1. Smoke detectors required by M606.2.1 and M606.2.3.

2. An approved area smoke detector system located in the return air plenum serving such units.

3. An area smoke detector system as prescribed in the exception to M606.2.1.

In all cases, the smoke detectors shall comply with M606.4 and M606.4.1.

M606.2.3 Return air risers. Where return air risers serve two or more stories and are part of a return air system having a design capacity greater than 15,000 cfm (7.1 m^3/s), smoke detectors shall be installed at each story. Such smoke detectors shall be located upstream of the connection between the return air riser and any air ducts or plenums.

M606.3 Installation. Smoke detectors required by this section shall be installed in accordance with NFPA 72. The required smoke detectors shall be installed to monitor the entire airflow conveyed by the system including return air and exhaust or relief air. Access shall be provided to smoke detectors for inspection and maintenance.

M606.4 Controls operation. Upon activation, the smoke detectors shall shut down the air distribution system. Air distribution systems that are part of a smoke control system shall switch to the smoke control mode upon activation of a detector.

M606.4.1 Supervision. The smoke detectors shall be connected to a fire alarm system. The actuation of a smoke detector shall activate a visible and audible supervisory signal at a constantly attended location.

EXCEPTIONS:

1. The supervisory signal at a constantly attended location is not required where the smoke detector activates the building's alarm-indicating appliances.

2. In occupancies not required to be equipped with a fire alarm system, actuation of a smoke detector shall activate a visible and an audible signal in an approved location. Smoke detector trouble conditions shall activate a visible or audible signal in an approved location and shall be identified as air duct detector trouble.