+---
+title: Gas Detection Systems
+category: Mechanical / Air Distribution
+toc_depth: 3
+description: >
+ When to use: Fixed gas detection equipment in buildings where code or safety mandates continuous or
+ demand-based atmospheric monitoring — enclosed and semi-enclosed parking garages (CO and NO2 for
+ occupant safety and ventilation demand control), refrigerant machinery rooms (refrigerant-concentration
+ detection triggering emergency ventilation and alarms per ASHRAE 15), commercial kitchen and food-service
+ mechanical rooms, and other occupied or semi-occupied mechanical spaces where NFPA 72, IBC, or the AHJ
+ mandates system-type detectors. Covers single- and multi-gas transmitter/sensor heads, control panels
+ and relay modules, audible/visual annunciators, and interlock wiring to ventilation or exhaust systems.
+ Not intended for: refrigerant piping, relief, and circuit leak-testing (use sync/refrigerant-piping);
+ supply ductwork and air distribution (use sync/hvac-ductwork, sync/hvac-air-distribution-devices); fans
+ the interlock activates (use sync/hvac-fans); BAS programming and DDC controllers fed by the relays (use
+ sync/building-automation-system); kitchen hood and grease exhaust (use sync/kitchen-exhaust-systems);
+ flame, smoke, and fire alarm notification appliances (use sync/fire-alarm-systems); portable or personal
+ gas monitors (not a fixed building system); industrial process analyzers and CEMS (use
+ sync/analytical-instrumentation); clean-agent discharge detection and abort stations (use
+ sync/clean-agent-fire-suppression).
+---
+
+# Scope {toc}
+
+## 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. {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. {note}
+
+## A gas detection system in this standard is distinct from a fire alarm system. {note}
+
+### The two systems may share annunciation pathways and notification appliances, but the gas detection function — sensing a target gas and interlocking ventilation — is a mechanical life-safety system in its own right, not a fire alarm initiating device, unless it is expressly integrated with the fire alarm control panel. {note}
+
+## Gas 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.
+
+## This standard applies to new construction and major renovation of commercial, institutional, industrial, and mixed-use projects.
+
+## The following are outside this standard and are governed elsewhere. {note}
+
+- Refrigerant piping, pressure relief, and leak-testing of refrigerant circuits are governed by [[sync/refrigerant-piping]].
+- Supply-air ductwork and air distribution devices are governed by [[sync/hvac-ductwork]] and [[sync/hvac-air-distribution-devices]].
+- Selection, drive sizing, and isolation of the ventilation fans that gas detection interlocks activate are governed by [[sync/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 [[sync/building-automation-system]].
+- Kitchen hood and grease-exhaust ventilation, including makeup air, is governed by [[sync/kitchen-exhaust-systems]].
+- Flame detectors, smoke detectors, and fire alarm notification appliances are governed by [[sync/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 [[sync/analytical-instrumentation]].
+- Clean-agent fire suppression discharge detection and abort stations are governed by [[sync/clean-agent-fire-suppression]].
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+## 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. {note}
+
+| 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 |
+
+# Submittals {toc}
+
+## Action Submittals {toc}
+
+### The 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.
+
+```datasheet
+label: Action submittals required
+type: checkbox
+options:
+ - 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
+```
+
+## Closeout Submittals {toc}
+
+### The 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.
+
+```datasheet
+label: Closeout submittals required
+type: checkbox
+options:
+ - 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
+```
+
+## Informational Submittals {toc}
+
+### The 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.
+
+```datasheet
+label: Informational submittals required
+type: checkbox
+options:
+ - Installer qualification / factory certification
+ - Calibration-gas traceability records
+```
+
+# Quality Assurance {toc}
+
+## Gas and vapor detectors shall be listed to UL 2075.
+
+### 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. {note}
+
+## Each sensor head, control module, and annunciator shall be listed to UL 2075 for its target gas and application.
+
+## Where 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.
+
+### 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. {note}
+
+## The control unit, where listed as a fire alarm control unit or auxiliary control for integration with a FACP, shall be listed to UL 864.
+
+## Startup, calibration, and the functional test shall be performed by a technician factory-certified by the equipment manufacturer.
+
+## A manufacturer's preliminary sensor layout shall be a required contract deliverable. {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. {note}
+
+# Environmental and Service Conditions {toc}
+
+## Sensor heads and panels shall be rated for the temperature, humidity, and washdown conditions of the space in which they are installed.
+
+## Where 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.
+
+### 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 [[sync/packaged-terminal-air-conditioners]] and [[sync/water-source-heat-pumps]] — carry their own machinery-room requirements under ASHRAE 15 addenda. Confirm the refrigerant and its group before selecting equipment ratings. {note}
+
+## In a classified machinery room, sensor heads, wiring methods, and enclosures shall be rated Class I, Division 2 per NEC Article 501.
+
+## Gas detection low-voltage wiring shall not share a conduit or raceway with line-voltage power circuits.
+
+### Routing detection signal wiring with line-voltage power violates the NEC separation rules and induces electromagnetic interference that produces nuisance alarms. Maintain separation per [[sync/grounding-and-bonding]] and the applicable raceway standard. {note}
+
+## The control panel shall annunciate loss of its 24 VDC supply power.
+
+### Unmonitored power loss leaves a space silently unprotected. Power-loss supervision is frequently omitted from specifications and is a required, not optional, function. {note}
+
+# Detection Scheme by Application {toc}
+
+## Parking Garage CO and NO2 Detection {toc}
+
+### Enclosed and semi-enclosed parking garages shall be monitored for both carbon monoxide and nitrogen dioxide.
+
+#### 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. {note}
+
+#### Carbon 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.
+
+#### Ventilation shall be activated when the CO concentration reaches the first-stage setpoint or the NO2 concentration reaches its first-stage setpoint, whichever occurs first.
+
+#### CO sensor heads shall be mounted at vehicle-exhaust level, 18 in. to 36 in. above the finished floor.
+
+#### NO2 sensor heads shall be mounted within 12 in. of the ceiling. {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. {note}
+
+```datasheet
+label: Parking garage gases monitored
+type: radio
+options:
+ - CO and NO2 (combined - default)
+ - CO only
+ - NO2 only
+default: CO and NO2 (combined - default)
+```
+
+```datasheet
+label: CO first-stage (ventilation) setpoint
+type: range
+unit: ppm
+min: 15
+max: 50
+step: 5
+default: 25
+```
+
+```datasheet
+label: CO second-stage (evacuation) setpoint
+type: range
+unit: ppm
+min: 35
+max: 100
+step: 5
+default: 50
+```
+
+```datasheet
+label: NO2 first-stage (ventilation) setpoint
+type: range
+unit: ppm
+min: 1
+max: 5
+step: 0.5
+default: 3
+```
+
+```datasheet
+label: CO sensor mounting height above finished floor
+type: range
+unit: in
+min: 18
+max: 36
+step: 6
+default: 18
+```
+
+```datasheet
+label: Sensor coverage area per head
+type: range
+unit: sq ft
+min: 5000
+max: 10000
+step: 1000
+default: 5000
+```
+
+## Refrigerant Machinery Room Detection {toc}
+
+### Each refrigeration machinery room shall contain a refrigerant detector serving the entire room per ASHRAE 15.
+
+#### 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. {note}
+
+#### The refrigerant detector first-stage (ventilation start) setpoint shall be set at or below the OEL value for the specific refrigerant in the system.
+
+#### The refrigerant detector second-stage (emergency alarm) setpoint shall be set at or below the RCL value for the specific refrigerant in the system.
+
+#### The detector shall be listed and factory-calibrated for the specific refrigerant designated by ASHRAE 34.
+
+##### 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. {note}
+
+#### Sensor 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.
+
+#### Audible and visual annunciation shall be provided both inside the machinery room and outside each entrance to the room.
+
+```datasheet
+label: Refrigerant detector sensor technology
+type: radio
+options:
+ - Infrared (NDIR or photoacoustic)
+ - Electrochemical
+ - Semiconductor
+default: Infrared (NDIR or photoacoustic)
+```
+
+```datasheet
+label: Refrigerant detector first-stage setpoint basis
+type: radio
+options:
+ - At or below refrigerant OEL (default)
+ - Manufacturer factory default for refrigerant
+default: At or below refrigerant OEL (default)
+```
+
+```datasheet
+label: Refrigerant sensor mounting height
+type: radio
+options:
+ - Within 12 in. of floor (denser than air - default)
+ - Within 12 in. of ceiling (lighter than air)
+default: Within 12 in. of floor (denser than air - default)
+```
+
+## Mechanical and Food-Service Room Detection {toc}
+
+### Commercial kitchen and food-service mechanical rooms shall be monitored for carbon monoxide, and for combustible gas where a fuel-gas supply is present. {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. {note}
+
+#### Where 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.
+
+##### 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. {note}
+
+#### CO 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.
+
+```datasheet
+label: Mechanical room gases monitored
+type: checkbox
+options:
+ - Carbon monoxide (CO)
+ - Combustible gas (LEL)
+```
+
+```datasheet
+label: CO detector type
+type: radio
+options:
+ - System-type (connected to FACP - default)
+ - Standalone CO alarm
+default: System-type (connected to FACP - default)
+```
+
+# Sensor Heads and Detection Technology {toc}
+
+## Sensor technology shall be matched to the target gas and application.
+
+### 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. {note}
+
+## Electrochemical CO and NO2 sensors shall have a T90 response time of 60 seconds or less.
+
+## Infrared refrigerant sensors shall have a T90 response time of 30 seconds or less.
+
+## Each sensor head shall provide a means of field calibration and a bump-test port or equivalent gas-introduction provision.
+
+## Sensors shall be replaced at or before their rated end of life.
+
+### 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. {note}
+
+## A 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.
+
+```datasheet
+label: Sensor technology - toxic gas (CO/NO2)
+type: radio
+options:
+ - Electrochemical
+ - Semiconductor
+default: Electrochemical
+```
+
+```datasheet
+label: Electrochemical sensor T90 response time (maximum)
+type: range
+unit: s
+min: 30
+max: 60
+step: 10
+default: 60
+```
+
+```datasheet
+label: Scheduled sensor replacement interval (electrochemical)
+type: range
+unit: years
+min: 2
+max: 5
+step: 1
+default: 3
+```
+
+```datasheet
+label: Field calibration interval
+type: radio
+options:
+ - Annual bump test, span calibration every 2 years (default)
+ - Annual bump test, annual span calibration
+ - Per manufacturer interval
+default: Annual bump test, span calibration every 2 years (default)
+```
+
+# System Architecture and Outputs {toc}
+
+## The 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.
+
+### 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. {note}
+
+## Relay outputs to ventilation equipment shall be coordinated with the actual input requirement of each fan starter or VFD. {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 [[sync/hvac-fans]]. {note}
+
+## Where the system reports to the BAS, the interface shall be BACnet/IP, BACnet MS/TP, or Modbus RTU as coordinated with [[sync/building-automation-system]].
+
+## Where a 4-20 mA analog output is provided to a DDC controller, each transmitter shall include a local display of the measured concentration.
+
+## The 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.
+
+```datasheet
+label: System architecture
+type: radio
+options:
+ - Standalone transmitter with integral relay
+ - Multi-point addressable control panel
+ - Network-enabled monitor (BAS-integrated)
+default: Multi-point addressable control panel
+```
+
+```datasheet
+label: Relay output to ventilation
+type: radio
+options:
+ - Dry-contact relay to fan starter / VFD (default)
+ - BACnet/IP or BACnet MS/TP
+ - Modbus RTU
+ - 4-20 mA analog to DDC controller
+default: Dry-contact relay to fan starter / VFD (default)
+```
+
+```datasheet
+label: Fan starter contact requirement
+type: radio
+options:
+ - Maintained (held) contact
+ - Momentary pulse
+default: Maintained (held) contact
+```
+
+```datasheet
+label: Control panel supply voltage
+type: radio
+options:
+ - 24 VDC
+ - 120 VAC with internal 24 VDC supply
+default: 24 VDC
+```
+
+```datasheet
+label: Backup power
+type: radio
+options:
+ - None
+ - Battery backup
+ - UPS backup
+default: Battery backup
+```
+
+# Alarm Annunciation and Interlocks {toc}
+
+## Alarms shall be staged into a first-stage warning and a second-stage emergency condition.
+
+### 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. {note}
+
+## A first-stage alarm shall start the associated ventilation or exhaust system.
+
+## A second-stage alarm shall annunciate an emergency condition and, where required by ASHRAE 15 or the AHJ, shut down the associated equipment.
+
+## Audible and visual annunciation shall be provided at the location required by the governing code for the application.
+
+## In a refrigerant machinery room, a remote annunciator shall be provided outside each entrance to the room.
+
+## Where annunciation is shared with the fire alarm system, the notification appliances and signal hierarchy shall be coordinated with [[sync/fire-alarm-systems]] and the fire alarm contractor.
+
+```datasheet
+label: Annunciation provided
+type: checkbox
+options:
+ - Local horn/strobe at sensor or panel
+ - Remote annunciator at room entrance
+ - Integrated with FACP notification appliances
+```
+
+```datasheet
+label: Second-stage action
+type: checkbox
+options:
+ - Emergency alarm annunciation
+ - Equipment shutdown
+ - Evacuation signaling
+```
+
+# Testing and Commissioning {toc}
+
+## A functional test shall be performed at startup for every sensor head.
+
+### 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. {note}
+
+## The functional test shall introduce calibration gas at each sensor head.
+
+## The functional test shall verify, within the specified response time, that the associated ventilation activates.
+
+## The functional test shall verify, within the specified response time, that the alarm annunciates.
+
+## The functional test shall verify, within the specified response time, that the corresponding BAS data point responds.
+
+## The functional test shall verify both the first-stage and second-stage action for each monitored gas.
+
+## A factory calibration certificate dated within the manufacturer's allowed interval before startup shall be furnished for each sensor head.
+
+## Power-loss supervision shall be tested by removing the 24 VDC supply and confirming that the panel annunciates the loss.
+
+```datasheet
+label: Commissioning functional test scope
+type: checkbox
+options:
+ - 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
+```
+
+# Installation {toc}
+
+## Sensor 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.
+
+## Sensor 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.
+
+## Sensor locations and routing shall follow [[drawing: gas detection plan]], and final field locations shall be recorded on the as-built drawings.
+
+## Conduit and raceway for detection wiring shall be installed separate from line-voltage power per the Environmental and Service Conditions section.
+
+## In a classified machinery room, all wiring methods and enclosures shall be installed to the NEC Class I, Division 2 requirements established for that room.
+
+## GFCI protection shall be provided for 125-volt receptacles serving detector maintenance where required by NEC Section 210.8, coordinated with [[sync/electrical-rooms]].
+
+## Duct-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.
+
+```datasheet
+label: Detection method
+type: radio
+options:
+ - Open-area sensor heads (default)
+ - Duct-sampling (ducted) detector
+default: Open-area sensor heads (default)
+```
+
+# Delivery, Storage, and Handling {toc}
+
+## Sensor 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.
+
+## Electrochemical sensors shall not be stored beyond the manufacturer's shelf interval before being placed in service. {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. {note}
+
+## Sensor heads shall be protected from construction dust, paint overspray, solvent vapors, and washdown during the remainder of construction.
+
+# Warranty {toc}
+
+## The Contractor shall warrant the gas detection system against defects in materials and workmanship for the specified warranty period from the date of substantial completion.
+
+## The 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.
+
+```datasheet
+label: System warranty period
+type: radio
+options:
+ - 1 year
+ - 2 years
+ - 3 years
+default: 1 year
+```
+
+```datasheet
+label: Sensor element warranty period
+type: radio
+options:
+ - 1 year
+ - 2 years
+default: 1 year
+```
+
+# Spare Parts {toc}
+
+## The Contractor shall furnish spare sensor elements for the toxic-gas detectors as a closeout deliverable, so the Owner can replace an expired or failed cell without waiting on procurement.
+
+## Spare sensor elements shall match the make, model, and calibration of the installed sensors.
+
+```datasheet
+label: Spare sensor elements furnished (per gas type)
+type: range
+unit: each
+min: 0
+max: 4
+step: 1
+default: 1
+```