1 Scope

NOTE This standard governs fixed gas detection systems that continuously or on demand monitor the atmosphere of an enclosed space and act on that measurement — annunciating an alarm, starting or modulating ventilation, or shutting down equipment. (1.1)

NOTE The four primary applications are enclosed and semi-enclosed parking garages (carbon monoxide and nitrogen dioxide), refrigerant machinery rooms (refrigerant-concentration detection per ASHRAE 15), commercial kitchen and food-service mechanical rooms (CO and combustible gas), and other occupied or semi-occupied mechanical spaces where the adopted code or the AHJ requires a system-type detector. (1.2)

NOTE A gas detection system in this standard is distinct from a fire alarm system. (1.3)

1.4Gas detection equipment shall be furnished, installed, wired, and commissioned as a complete operating system, including sensor heads, control or relay modules, annunciators, interlock wiring, and field calibration.

1.5This standard applies to new construction and major renovation of commercial, institutional, industrial, and mixed-use projects.

NOTE The following are outside this standard and are governed elsewhere. (1.6)

Refrigerant piping, pressure relief, and leak-testing of refrigerant circuits are governed by Refrigerant Piping.
Supply-air ductwork and air distribution devices are governed by Hvac Ductwork and Hvac Air Distribution Devices.
Selection, drive sizing, and isolation of the ventilation fans that gas detection interlocks activate are governed by Hvac Fans.
BAS network topology, DDC controller selection, and the control logic that the gas detection relays or BACnet/Modbus outputs feed are governed by Building Automation System.
Kitchen hood and grease-exhaust ventilation, including makeup air, is governed by Kitchen Exhaust Systems.
Flame detectors, smoke detectors, and fire alarm notification appliances are governed by Fire Alarm Systems.
Portable or personal gas monitors, bump-test equipment, and confined-space monitors are not permanently installed building systems and are outside this standard.
Industrial process gas analyzers and continuous emissions monitoring are governed by Analytical Instrumentation.
Clean-agent fire suppression discharge detection and abort stations are governed by Clean Agent Fire Suppression.

2 Referenced Standards

2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.

2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

NOTE The edition of the IMC, IBC, IFC, and NEC in force is the edition adopted by the Authority Having Jurisdiction, which may lag the most recent published edition. (2.3)

Standard	Title
UL 2075	Gas and Vapor Detectors and Sensors
UL 864	Control Units and Accessories for Fire Alarm Systems
ANSI/ASHRAE 15-2022	Safety Standard for Refrigeration Systems
ANSI/ASHRAE 34-2022	Designation and Safety Classification of Refrigerants
ANSI/ASHRAE 62.1-2022	Ventilation and Acceptable Indoor Air Quality
NFPA 72	National Fire Alarm and Signaling Code
NFPA 70 (NEC)	National Electrical Code (Articles 500, 501, 210.8)
IBC	International Building Code (Section 915, Carbon Monoxide Detection)
IMC	International Mechanical Code (Section 404, Enclosed Parking Garages)
OSHA 29 CFR 1910.1000	Air Contaminants — Permissible Exposure Limits

3 Submittals

3.1 Action Submittals

3.1.1The Contractor shall submit the following action submittals for review before fabrication or ordering:

Product data for each sensor head, control or relay module, and annunciator, including UL 2075 listing, sensor technology, target gas, measuring range, and T90 response time.
A manufacturer's preliminary sensor layout drawing showing each sensor head location, mounting height, coverage area, and the basis (manufacturer listing or AHJ requirement) for the spacing used.
A wiring and interconnection diagram showing sensor-to-panel wiring, power source, relay output assignments, and the interlock connection to each ventilation fan, exhaust fan, or VFD.
A points list and protocol declaration where the system integrates with the BAS, identifying each BACnet object or Modbus register and its engineering units.
An alarm setpoint schedule listing the first-stage and second-stage setpoint for each gas and the resulting action (ventilation start, local alarm, remote alarm, equipment shutdown).
For refrigerant detection, the refrigerant ASHRAE 34 designation, its OEL and RCL values, and confirmation that each detector is listed and calibrated for that refrigerant.

Action submittals requiredcheckbox

☐ Product data (each sensor, panel, annunciator)

☐ Manufacturer preliminary sensor layout drawing

☐ Wiring and interconnection diagram

☐ BAS points list and protocol declaration

☐ Alarm setpoint schedule

☐ Refrigerant designation, OEL/RCL, detector listing

3.2 Closeout Submittals

3.2.1The Contractor shall submit the following closeout submittals before final acceptance:

Factory calibration certificates for each sensor head, dated within the manufacturer's allowed shelf interval before startup.
A field functional test report documenting calibration-gas verification at each sensor head and the measured response of ventilation, alarm annunciation, and BAS data points.
Operation and maintenance manuals including sensor replacement intervals, calibration procedure, and the bump-test method.
A record (as-built) drawing showing final sensor locations, mounting heights, and wiring routing.
A sensor replacement schedule identifying the end-of-life date of each electrochemical and infrared sensor.

Closeout submittals requiredcheckbox

☐ Factory calibration certificates (each sensor)

☐ Field functional test report

☐ Operation and maintenance manuals

☐ Record (as-built) drawings

☐ Sensor replacement schedule with end-of-life dates

3.3 Informational Submittals

3.3.1The Contractor shall submit the following informational submittals:

Manufacturer's installer qualification or factory certification for the technician performing startup and calibration.
Field test instrument calibration traceability for the calibration-gas cylinders and flow regulators used at startup.

Informational submittals requiredcheckbox

☐ Installer qualification / factory certification

☐ Calibration-gas traceability records

4 Quality Assurance

4.1Gas and vapor detectors shall be listed to UL 2075.

NOTE UL 2075 is the listing standard for CO, NO2, and refrigerant gas detectors, and the IMC mandates UL 2075 listing for all detectors in enclosed parking structures. A non-listed detector is not code-compliant for those applications, and many imported units lack the listing — confirm it on the product data, not the catalog page. (4.1.1)

4.2Each sensor head, control module, and annunciator shall be listed to UL 2075 for its target gas and application.

4.3Where the gas detection system interfaces with a fire alarm control panel, the control unit shall be listed to UL 864 or the interface shall be made through a listed relay module.

NOTE Specifying a non-listed interface between gas detection and the fire alarm control panel is a common cause of fire alarm submittal rejection. The listing requirement is on the interface, not only the panel. (4.3.1)

4.4The control unit, where listed as a fire alarm control unit or auxiliary control for integration with a FACP, shall be listed to UL 864.

4.5Startup, calibration, and the functional test shall be performed by a technician factory-certified by the equipment manufacturer.

NOTE A manufacturer's preliminary sensor layout shall be a required contract deliverable. (4.6)

NOTE Manufacturer representatives routinely provide free submittal and layout assistance. Requiring a preliminary layout as a deliverable transfers the spacing and mounting-height responsibility to the party with the listing data and removes a frequent source of field rework. (4.6.1)

5 Environmental and Service Conditions

5.1Sensor heads and panels shall be rated for the temperature, humidity, and washdown conditions of the space in which they are installed.

5.2Where a refrigerant machinery room uses an A2, A3, B2, or B3 refrigerant, the room is a classified location and electrical equipment shall comply with NEC Article 500 and 501 for Class I, Division 2.

NOTE The ASHRAE 34 safety group of the refrigerant determines whether hazardous-location classification applies. A1 and B1 refrigerants do not by themselves classify the room; A2L refrigerants — now appearing in equipment per Packaged Terminal Air Conditioners and Water Source Heat Pumps — carry their own machinery-room requirements under ASHRAE 15 addenda. Confirm the refrigerant and its group before selecting equipment ratings. (5.2.1)

5.3In a classified machinery room, sensor heads, wiring methods, and enclosures shall be rated Class I, Division 2 per NEC Article 501.

NOTE Routing detection signal wiring with line-voltage power violates the NEC separation rules and induces electromagnetic interference that produces nuisance alarms. Maintain separation per Grounding And Bonding and the applicable raceway standard. (5.4.1)

5.5The control panel shall annunciate loss of its 24 VDC supply power.

NOTE Unmonitored power loss leaves a space silently unprotected. Power-loss supervision is frequently omitted from specifications and is a required, not optional, function. (5.5.1)

6 Detection Scheme by Application

6.1 Parking Garage CO and NO2 Detection

6.1.1Enclosed and semi-enclosed parking garages shall be monitored for both carbon monoxide and nitrogen dioxide.

NOTE The IMC requires both CO and NO2 detection in enclosed parking garages regardless of fleet type. Specifying CO-only detection for a garage serving an electric-vehicle or hybrid-heavy fleet is a defect — EV-dominant garages produce negligible CO but still see NO2 from diesel delivery vehicles, and the code does not waive the NO2 requirement. (6.1.1.1)

6.1.1.2Carbon monoxide detectors and nitrogen dioxide sensors shall be listed to UL 2075 and shall serve as the basis for demand-controlled or continuously operated mechanical ventilation.

6.1.1.3Ventilation shall be activated when the CO concentration reaches the first-stage setpoint or the NO2 concentration reaches its first-stage setpoint, whichever occurs first.

6.1.1.4CO sensor heads shall be mounted at vehicle-exhaust level, 18 in. to 36 in. above the finished floor.

NOTE NO2 sensor heads shall be mounted within 12 in. of the ceiling. (6.1.1.5)

NOTE NO2 does not behave as a simple heavier-than-air gas in this context; the warm exhaust plume carrying it rises, so NO2 sensors belong near the ceiling and CO sensors belong at exhaust level. Reversing the two heights invalidates the detection scheme even though the equipment tests fine on the bench. (6.1.1.5.1)

Parking garage gases monitoredradio

● CO and NO2 (combined - default)

○ CO only

○ NO2 only

CO first-stage (ventilation) setpointrange

ppm

1550

Default: 25 ppm

CO second-stage (evacuation) setpointrange

ppm

35100

Default: 50 ppm

NO2 first-stage (ventilation) setpointrange

ppm

15

Default: 3 ppm

CO sensor mounting height above finished floorrange

in

1836

Default: 18 in

Sensor coverage area per headrange

sq ft

500010000

Default: 5000 sq ft

6.2 Refrigerant Machinery Room Detection

6.2.1Each refrigeration machinery room shall contain a refrigerant detector serving the entire room per ASHRAE 15.

NOTE ASHRAE 15 requires a refrigerant detector in every machinery room, with a first-stage alarm that starts emergency ventilation and a second-stage alarm that annunciates an emergency condition and may shut down equipment. (6.2.1.1)

6.2.1.2The refrigerant detector first-stage (ventilation start) setpoint shall be set at or below the OEL value for the specific refrigerant in the system.

6.2.1.3The refrigerant detector second-stage (emergency alarm) setpoint shall be set at or below the RCL value for the specific refrigerant in the system.

6.2.1.4The detector shall be listed and factory-calibrated for the specific refrigerant designated by ASHRAE 34.

NOTE A generic "refrigerant detector" called out on a drawing is insufficient and generates an RFI. The detector must be calibrated and listed for the exact refrigerant in the circuit, because the OEL, the RCL, and the sensor response all depend on the refrigerant. Name the refrigerant by its ASHRAE 34 designation. (6.2.1.4.1)

6.2.1.5Sensor mounting height shall be selected by refrigerant density relative to air: refrigerants denser than air shall be detected within 12 in. of the floor, and refrigerants lighter than air shall be detected within 12 in. of the ceiling.

6.2.1.6Audible and visual annunciation shall be provided both inside the machinery room and outside each entrance to the room.

Refrigerant detector sensor technologyradio

● Infrared (NDIR or photoacoustic)

○ Electrochemical

○ Semiconductor

Refrigerant detector first-stage setpoint basisradio

● At or below refrigerant OEL (default)

○ Manufacturer factory default for refrigerant

Refrigerant sensor mounting heightradio

● Within 12 in. of floor (denser than air - default)

○ Within 12 in. of ceiling (lighter than air)

6.3 Mechanical and Food-Service Room Detection

NOTE Commercial kitchen and food-service mechanical rooms shall be monitored for carbon monoxide, and for combustible gas where a fuel-gas supply is present. (6.3.1)

NOTE Combustible-gas detection in these spaces is based on the lower explosive limit (LEL) and is intended to alarm and act well before a flammable atmosphere develops, not at the exposure limits used for toxic gases. (6.3.1.1)

6.3.1.2Where IBC Section 915 requires system-type CO detectors connected to a fire alarm panel, the detectors shall be system-type rather than standalone CO alarms.

NOTE IBC Section 915 distinguishes a system-type CO detector — connected to and supervised by a fire alarm control unit — from a standalone CO alarm. The two are not interchangeable where the code calls for the system type. (6.3.1.2.1)

6.3.1.3CO detectors in occupied or semi-occupied mechanical spaces shall be placed and spaced per NFPA 72 where the detectors are integrated with the fire alarm control panel.

Mechanical room gases monitoredcheckbox

☐ Carbon monoxide (CO)

☐ Combustible gas (LEL)

CO detector typeradio

● System-type (connected to FACP - default)

○ Standalone CO alarm

7 Sensor Heads and Detection Technology

7.1Sensor technology shall be matched to the target gas and application.

NOTE Electrochemical cells are the standard for CO, NO2, and other toxic gases; non-dispersive infrared (NDIR) and photoacoustic infrared are standard for refrigerants and CO2; catalytic bead is standard for combustible (LEL) gases; and semiconductor sensors are a lower-cost, lower-accuracy option. Select the technology by gas before selecting a product. (7.1.1)

7.2Electrochemical CO and NO2 sensors shall have a T90 response time of 60 seconds or less.

7.3Infrared refrigerant sensors shall have a T90 response time of 30 seconds or less.

7.4Each sensor head shall provide a means of field calibration and a bump-test port or equivalent gas-introduction provision.

7.5Sensors shall be replaced at or before their rated end of life.

NOTE Electrochemical CO and NO2 cells have a typical life of 2 to 5 years; infrared refrigerant sensors typically last 5 to 10 years. Buildings routinely operate with expired sensors because no replacement interval was specified. A scheduled replacement at the conservative end of the electrochemical range keeps the system within its rated accuracy. (7.5.1)

7.6A full span calibration shall be performed every one to two years, or at the manufacturer's stated interval, and at minimum an annual field bump test shall be performed.

Sensor technology - toxic gas (CO/NO2)radio

● Electrochemical

○ Semiconductor

Electrochemical sensor T90 response time (maximum)range

s

3060

Default: 60 s

Scheduled sensor replacement interval (electrochemical)range

years

25

Default: 3 years

Field calibration intervalradio

● Annual bump test, span calibration every 2 years (default)

○ Annual bump test, annual span calibration

○ Per manufacturer interval

8 System Architecture and Outputs

8.1The system architecture shall be selected from a standalone transmitter with integral relay, a multi-point addressable control panel, or a network-enabled monitor integrated with the BAS.

NOTE A standalone transmitter with an integral relay suits a single-zone space; a multi-point addressable panel with zone assignments suits a multi-zone garage; a network-enabled monitor reporting over BACnet/IP or Modbus RTU suits direct BAS integration without a dedicated panel. The choice follows zone count and whether the BAS owns the control logic. (8.1.1)

NOTE Relay outputs to ventilation equipment shall be coordinated with the actual input requirement of each fan starter or VFD. (8.2)

NOTE Some fan starters require a maintained (held) contact and others require a momentary pulse. A mismatched relay output causes ventilation to fail during acceptance testing even though every device works in isolation. Confirm the required contact behavior against the fan control per Hvac Fans. (8.2.1)

8.3Where the system reports to the BAS, the interface shall be BACnet/IP, BACnet MS/TP, or Modbus RTU as coordinated with Building Automation System.

8.4Where a 4-20 mA analog output is provided to a DDC controller, each transmitter shall include a local display of the measured concentration.

8.5The control panel shall be powered from a dedicated 24 VDC supply, and where required by the AHJ the supply shall include battery or UPS backup for the specified duration.

System architectureradio

○ Standalone transmitter with integral relay

● Multi-point addressable control panel

○ Network-enabled monitor (BAS-integrated)

Relay output to ventilationradio

● Dry-contact relay to fan starter / VFD (default)

○ BACnet/IP or BACnet MS/TP

○ Modbus RTU

○ 4-20 mA analog to DDC controller

Fan starter contact requirementradio

● Maintained (held) contact

○ Momentary pulse

Control panel supply voltageradio

● 24 VDC

○ 120 VAC with internal 24 VDC supply

Backup powerradio

○ None

● Battery backup

○ UPS backup

9 Alarm Annunciation and Interlocks

9.1Alarms shall be staged into a first-stage warning and a second-stage emergency condition.

NOTE The first stage is a warning that activates ventilation and alerts occupants; the second stage is an emergency condition that drives evacuation signaling and, where applicable, equipment shutdown. Both stages must be defined for every monitored gas. (9.1.1)

9.2A first-stage alarm shall start the associated ventilation or exhaust system.

9.3A second-stage alarm shall annunciate an emergency condition and, where required by ASHRAE 15 or the AHJ, shut down the associated equipment.

9.4Audible and visual annunciation shall be provided at the location required by the governing code for the application.

9.5In a refrigerant machinery room, a remote annunciator shall be provided outside each entrance to the room.

9.6Where annunciation is shared with the fire alarm system, the notification appliances and signal hierarchy shall be coordinated with Fire Alarm Systems and the fire alarm contractor.

Annunciation providedcheckbox

☐ Local horn/strobe at sensor or panel

☐ Remote annunciator at room entrance

☐ Integrated with FACP notification appliances

Second-stage actioncheckbox

☐ Emergency alarm annunciation

☐ Equipment shutdown

☐ Evacuation signaling

10 Testing and Commissioning

10.1A functional test shall be performed at startup for every sensor head.

NOTE The functional test is the only proof that the installed system actually does what it was specified to do. Omitting it leaves the system unverified at turnover, which is one of the most common defects in gas detection projects. (10.1.1)

10.2The functional test shall introduce calibration gas at each sensor head.

10.3The functional test shall verify, within the specified response time, that the associated ventilation activates.

10.4The functional test shall verify, within the specified response time, that the alarm annunciates.

10.5The functional test shall verify, within the specified response time, that the corresponding BAS data point responds.

10.6The functional test shall verify both the first-stage and second-stage action for each monitored gas.

10.7A factory calibration certificate dated within the manufacturer's allowed interval before startup shall be furnished for each sensor head.

10.8Power-loss supervision shall be tested by removing the 24 VDC supply and confirming that the panel annunciates the loss.

Commissioning functional test scopecheckbox

☐ Calibration gas applied at each sensor head

☐ Ventilation activation verified

☐ Alarm annunciation verified

☐ BAS data point response verified

☐ First- and second-stage actions verified

☐ Power-loss supervision verified

11 Installation

11.1Sensor heads shall be installed at the mounting height required for their gas and application, and at the coverage spacing established by the manufacturer's listed layout and the AHJ.

11.2Sensor heads shall be located to represent the breathing or accumulation zone of the target gas and shall be kept clear of supply-air diffusers, doors, and other sources of local air movement that would bias the reading.

11.3Sensor locations and routing shall follow gas detection plan, and final field locations shall be recorded on the as-built drawings.

11.4Conduit and raceway for detection wiring shall be installed separate from line-voltage power per the Environmental and Service Conditions section.

11.5In a classified machinery room, all wiring methods and enclosures shall be installed to the NEC Class I, Division 2 requirements established for that room.

11.6GFCI protection shall be provided for 125-volt receptacles serving detector maintenance where required by NEC Section 210.8, coordinated with Electrical Rooms.

11.7Duct-sampling detectors, where used in lieu of open-area detection, shall be installed with a separately listed duct-sampling assembly on the return-air or exhaust-air stream.

Detection methodradio

● Open-area sensor heads (default)

○ Duct-sampling (ducted) detector

12 Delivery, Storage, and Handling

12.1Sensor heads shall be delivered in the manufacturer's sealed packaging and shall be stored within the temperature and humidity range stated by the manufacturer until installation.

NOTE Electrochemical sensors shall not be stored beyond the manufacturer's shelf interval before being placed in service. (12.2)

NOTE Electrochemical cells age on the shelf as well as in service. A sensor that sat in storage too long before commissioning starts its field life already partly consumed, which shortens the interval to first replacement. (12.2.1)

12.3Sensor heads shall be protected from construction dust, paint overspray, solvent vapors, and washdown during the remainder of construction.

13 Warranty

13.1The Contractor shall warrant the gas detection system against defects in materials and workmanship for the specified warranty period from the date of substantial completion.

13.2The sensor element warranty shall be stated separately from the equipment warranty, because consumable electrochemical and infrared sensors carry a shorter rated life than the panel and transmitters.

System warranty periodradio

● 1 year

○ 2 years

○ 3 years

Sensor element warranty periodradio