Smoke detector

Not to be confused with Smoke alarm.

A smoke detector is a device that detects smoke. Smoke detectors are typically used as initiating devices on fire alarm systems, although in certain cases they may also operate standalone.

Operation

Smoke detectors require power to operate automatically. For two wire conventional detectors, this means they cannot create a short circuit or they will not function. Instead, upon activation, they have an increase in current flow which the panel will still see as enough to activate, but the detector allows for enough power to keep it and sometimes other detectors active.

Four wire detectors work a bit differently, and more often than not are seen on security systems rather than fire, but it is still good to know. Four wire detectors take in both external power, and the IDC (Zone) wires separately. This means that when the detector activates, it causes a short on the IDC, but still has full operation power.

Intelligent detectors work very differently from conventional detectors. For the most part, these are more of sensors than anything. The panel is constantly getting a reading from the detector, and at a certain chamber value, this will cause an alarm. It's designed to be very simple, but this technology allows modern panels to decide when the detector activates, rather than let the detector decide. This can reduce false alarms.

Furthermore, intelligent detectors are smart enough to know when they need to be cleaned, and will send a trouble to the panel to let the panel know it needs to be cleaned. This again reduces false alarms, as a dirty conventional detector will often just go into alarm.

Coverage types

Beam smoke detectors

A beam smoke detector is considered equivalent to a row of spot-type smoke detectors.

Aspirating smoke detectors

Each sampling port of an aspirating smoke detector is generally considered equivalent to a spot-type smoke detector.

Duct smoke detectors

Smoke detectors may be installed inside ducts to control HVAC shutdown.

Open area protection

Open area protection may be provided using spot-type, beam, or aspirating smoke detectors. NFPA 72 includes prescriptive requirements for detector spacing, but performance-based alternatives may also be used.

NFPA's main codes have numerous requirements and reductions for open area protection:

• Smoke detection is required when an exit enclosure provides access to a mechanical room.
• Elevator lobbies must be provided with smoke detection if their exit access doors are normally locked against egress.
• Smoke detection must cover 75 feet around non-egress revolving doors whose collapsing force exceeds 180 lb.
• Partial smoke detection is required in certain parts of airport traffic control towers, with more coverage required if the tower has a single exit.
• Fire-rated construction may be omitted from corridors and lobbies in new assembly occupancies if the building is fully covered with smoke detection.
• New underground/limited access assembly occupancies more than 30 feet below the discharge level must be covered with smoke detection that is connected to a smoke control system.
• Smoke detection must be provided above stages in assembly occupancies for the purpose of initiating smoke control.
• Special amusement buildings must be provided with smoke detection systems, especially when there are low light levels.
• Smoke detection is required in sufficiently large vehicles and boats on display in museums.
• Several conditions may lead to the installation of smoke detectors specifically in corridors.
  • Clothing may be stored in corridors of assembly, educational, and day care occupancies if smoke detection is provided.
  • Corridors serving new day care homes require smoke detection systems if the corridors belong to other occupancies, unless sufficient smoke alarms are installed, including in the corridor.
  • Pull stations may be eliminated from educational occupancies under certain conditions, one of which being the presence of smoke detection in corridors.
  • Existing hotels and dormitories may have transoms, louvers, and transfer grille when the corridors are protected by smoke detection.
• Smoke detection is required in day care occupancies except single-room occupancies that open directly to the outside. Existing day care occupancies may also omit smoke detection if occupants are capable of self preservation.
• Existing day care occupancies may have one of their two required exits unenclosed if smoke detection is provided on the discharge level and the level below it.
• Smoke detection must be provided in (ambulatory) health care spaces locked against egress for patient protection, unless staff can remotely unlock the doors at a constantly attended location. This requirement does not apply to spaces that require heavier security.
• Smoke detection must be provided in exit corridors of health care occupancies if fixed furniture is installed, unless there is direct staff supervision.
• Exit accesses from patient rooms of health care occupancies may pass through one intervening room with smoke detection before reaching a corridor; this requirement does not apply to existing buildings if the contents of the room are deemed to not pose a significant hazard.
• Smoke detection is required in hazardous areas of new health care suites if those areas are not separated from the remainder of the suite.
• Smoke detection is required in all patient sleeping rooms that are not provided with constant staff supervision, and in sleeping suites larger than 7500 square feet, such smoke detection must extend to the entire suite.
• Smoke detection is required in non sleeping patient care suites greater than 12500 square feet.
• New nursing homes must provide smoke detection in either corridors or patient rooms.
• With some exceptions, if a space of a health care occupancy opens to a corridor, then the corridor requires either a smoke detection or quick-response sprinkler system, and the open space requires a smoke detection system if it is not constantly supervised by staff.
• Smoke detection is required in rooms of existing health care occupancies occupied by patients if the construction type is of lower safety, unless the sprinklers are quick-response.
• In existing health care occupancies, non sleeping patient care suites greater than 10000 square feet must either have sprinkler systems or smoke detection systems, and both must be provided when the suite size exceeds 12500 square feet.
• Corridors of existing limited care facilities must have smoke detection unless the corridors serve patient sleeping rooms that are protected by smoke detection.
• The flammability restrictions on furniture and mattresses in existing health care occupancies are reduced when smoke detection or smoke alarms are provided.
• Ambulatory health care occupancies are not required to be separated into multiple smoke compartments if they are sufficiently small and have smoke detection.
• Detention/correctional occupancies must be covered with smoke detection, excluding some small sleeping rooms and Use Condition II dormitories with staff constantly present.
• Lockups in buildings require smoke detection systems.
• One- and two-family homes must be provided with either smoke alarms or smoke detection systems.
• Smoke detection is required in new hotels and dormitories not protected by sprinklers.
• Smoke detectors are required in all common areas of existing apartment buildings utilizing Option 2.
• New residential board and care occupancies with more than 16 residents and those without secondary means of escape require smoke detection in interior corridors and spaces open to such corridors.
• Smoke alarms may be omitted from existing residential board and care occupancies with more than 16 residents if smoke detection is provided in the corridors, and non-sleeping rooms do not require access to a separated exit if smoke detection is provided and the contents are determined to not be overly hazardous.
• Existing residential board and care occupancies with more than 16 residents must have smoke detection in all enclosed corridors, as well as living areas unless the building is sprinklered and the occupants are sufficiently capable of evacuating.
• Existing small business occupancies may be provided with a single exit if the building is protected by sprinklers and smoke detection.

IBC also has several requirements for smoke detection.

• Smoke detection is required in high rise buildings.
• Sleeping rooms in I-2 care suites must be provided with smoke detection if they are used as exit access for more than 8 beds and care providers are unable to supervise the suites, as well as care suites greater than 7500 square feet.
• Non sleeping I-2 care suites greater than 12500 square feet must have smoke detection.
• Group I-2 occupancies must provide smoke detection in either sleeping rooms or corridors when the sleeping rooms are permitted to be open to the corridors.
• Smoke detection is required in special amusement areas.
• Smoke detection is required in airport traffic control towers.
• Equipment areas of sprinklered telecommunication buildings must be provided with smoke detection if they are not protected by sprinklers.
• Smoke detection is required in ambulatory care occupancies, except those by supervised sprinklers.
• Pull stations may be omitted from Group E occupancies if certain alternative conditions are met, including the presence of smoke detection in corridors.
• Smoke detection is required in Group I-1 occupancies excluding sleeping areas and kitchens. Condition 1 occupancies may reduce this to corridors and waiting areas open to corridors if they are sprinklered.
• Smoke detection is required in Group I-3 occupancies excluding small sprinklered sleeping units.
• Smoke detection is required in interior corridors of Group R-1 occupancies, if such corridors exist.
• Smoke detection is required in Group R-2 university buildings in common areas, laundry rooms, and interior corridors, unless the building does not have interior corridors.
• Buildings with controlled egress doors must be covered with either sprinkler systems or smoke detection systems.
• Smoke detection must cover 75 feet around non-egress revolving doors with breakout forces exceeding 180 lb.

Other detector locations

Door closers

Smoke detectors are often installed near fire doors to close the doors in the presence of smoke.

Dwelling units

Smoke detectors are often permitted to be used in place of smoke alarms in dwelling units, provided that they are arranged to provide equivalent functionality. This is typically accomplished by mounting the smoke detector on a sounder base or using a smoke detector with an integral horn.

Elevators

Smoke detectors are often installed around elevators to control elevator recall.

Fire alarm system protection

Smoke detectors are typically installed above the FACP and other critical components of the fire alarm system to increase the likelihood of an alarm being transmitted before the system itself can be damaged by a fire. NFPA 72 and the I-Codes require a smoke detector to be installed above every FACP, power supply, and communicator located in an area not continuously occupied, unless ambient conditions prohibit the use of a smoke detector, in which case a heat detector is permitted.

HVAC shutdown

Smoke detectors are often required to be installed inside ducts for HVAC shutdown, but the requirement generally does not apply if smoke detectors are installed for open area protection.