Gas detection,
enclosed garages.
An enclosed parking garage is a box that collects vehicle exhaust. The code answer to that is mechanical ventilation, and the practical answer is gas detection that runs the ventilation only when it is needed. This page explains how those systems are built, what the codes expect, and where they go wrong.
What the system is made of
- Sensors. Electrochemical CO cells, plus NO2 sensors where diesel traffic is present. They are consumable: the cell degrades with exposure and age, and its output drifts.
- A controller or panel. Reads the sensors, applies setpoints, drives relays. Common equipment in the garages we service includes Conspec Controls, Macurco and CET, along with Honeywell, Intec and others.
- Ventilation interlock. Relay or BAS output that starts exhaust fans, often through a variable frequency drive so fans ramp instead of hard starting.
- Alarms and signalling. Local horn or strobe, and in many buildings a supervisory or alarm signal to the fire alarm panel.
What the codes require
IBC 406.4.2 requires mechanical ventilation for enclosed parking garages, which may run continuously or be controlled automatically by carbon monoxide detection. California Fire Code 916.11 requires gas detection systems to be inspected and tested at least annually, with each sensor calibrated at its manufacturer’s interval. Cal/OSHA Title 8 section 5155 sets the exposure limit the system exists to hold, 25 ppm over 8 hours. More on all three on our code requirements page.
Sensor placement matters more than sensor count
CO is close to the density of air, so it does not simply sink or rise, it goes where the airflow takes it. Sensors belong in the places where exhaust accumulates and people linger: near ramps and idling queues, in dead-end bays, in low corners away from supply air, at breathing height rather than at the ceiling. Sensors mounted where it was easy to run conduit, directly in front of a supply fan or right next to an open exterior wall, will read clean while the far corner of the garage does not.
Ventilation control is where the money is
A garage with no working detection has to run its fans continuously. With functioning detection and VFD control, the fans run a small fraction of the day and ramp with demand. That is the energy case for keeping the system healthy, and it is also why a drifted sensor shows up on a utility bill before it shows up on an inspection: a sensor reading high holds the fans on 24/7.
How these systems fail
- Sensors well past their calibration interval, reading whatever they have drifted to
- Replacement sensors dropped in without a calibration in place
- Fan interlock never tested, so nobody knows the relay still starts the fans
- Panels in fault with the buzzer disabled, which is the beeping call nobody wants at 2am
- Obsolete panels where sensors are no longer available, which becomes a retrofit rather than a repair
What service should look like
A real visit puts certified span gas on every sensor, records the as found reading before adjustment, verifies the fan interlock and alarm outputs, and leaves a dated report per sensor. That is what our calibration visit covers, and what an inspector wants to see.
Talk to us
Gas monitoring is the only thing we do. Tell us the building and roughly how many sensors are in the garage, or send a photo of the panel, and we will tell you what it needs.
Common questions
What counts as an enclosed parking garage?
Broadly, a garage that does not have enough permanent openings to ventilate naturally, so basement and podium parking, structures wrapped on all sides, and any level below grade. Those are the garages that need mechanical ventilation, and therefore the ones where gas detection controls the fans.
Do we need NO2 detection as well as CO?
It depends on the traffic. Diesel vehicles produce nitrogen dioxide, so garages serving trucks, shuttles, loading docks or drive-in warehouses commonly monitor NO2 alongside CO. Passenger-car-only garages are usually CO only.
How many sensors does a garage need?
It is driven by area, layout and airflow rather than a single ratio, and columns, ramps and separate fan zones all matter. Real garages we service commonly run 10 to 20 sensors, and large structures run well over that.
How often do the sensors need calibration?
At the interval the manufacturer specifies, usually every 6 to 12 months, and the system has to be inspected and tested at least annually. Electrochemical CO cells drift as they age, which is why calibration is not optional maintenance.
Talk to a gas monitoring specialist
Tell us the building and how many sensors you have. We will tell you what service it needs and what it costs, no pressure.