Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Gas Detection Systems
…139 unchanged lines
## 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}
+## A manufacturer's preliminary sensor layout shall be a required contract deliverable.
### 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}
…23 unchanged lines
### 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
…6 unchanged lines
```
+#### 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.
+
```datasheet
label: CO first-stage (ventilation) setpoint
…6 unchanged lines
```
+#### 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.
+
+##### 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}
+
+##### The CO second-stage evacuation setpoint shall be specified, set above the first-stage ventilation setpoint to trigger occupant alarm and evacuation.
+
```datasheet
label: CO second-stage (evacuation) setpoint
…26 unchanged lines
```
+##### The gas detector coverage area per sensing head shall be specified, with CO and NO2 heads positioned at the mounting height appropriate to each gas.
+
```datasheet
label: Sensor coverage area per head
…38 unchanged lines
type: radio
options:
− - At or below refrigerant OEL (default)
+ - At or below refrigerant OEL
- Manufacturer factory default for refrigerant
−default: At or below refrigerant OEL (default)
+default: At or below refrigerant OEL
```
…9 unchanged lines
## 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}
+### Commercial kitchen and food-service mechanical rooms shall be monitored for carbon monoxide, and for combustible gas where a fuel-gas supply is present.
#### 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}
…73 unchanged lines
type: radio
options:
− - Annual bump test, span calibration every 2 years (default)
+ - Annual bump test, span calibration every 2 years
- Annual bump test, annual span calibration
- Per manufacturer interval
−default: Annual bump test, span calibration every 2 years (default)
+default: Annual bump test, span calibration every 2 years
```
…4 unchanged lines
### 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}
+## Relay outputs to ventilation equipment shall be coordinated with the actual input requirement of each fan starter or VFD.
### 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}
…19 unchanged lines
type: radio
options:
− - Dry-contact relay to fan starter / VFD (default)
+ - Dry-contact relay to fan starter / VFD
- BACnet/IP or BACnet MS/TP
- Modbus RTU
- 4-20 mA analog to DDC controller
−default: Dry-contact relay to fan starter / VFD (default)
+default: Dry-contact relay to fan starter / VFD
```
…112 unchanged lines
type: radio
options:
− - Open-area sensor heads (default)
+ - Open-area sensor heads
- Duct-sampling (ducted) detector
−default: Open-area sensor heads (default)
+default: Open-area sensor heads
```
…2 unchanged lines
## 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 sensors shall not be stored beyond the manufacturer's shelf interval before being placed in service.
### 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}
…41 unchanged lines
default: 1
```