Cal/OSHA 5155
and CO.
Most people managing a parking garage meet Cal/OSHA section 5155 the hard way: an employee who spends their shift in the garage complains about headaches, or an inspector asks what the carbon monoxide level is and nobody can answer. This page covers what the rule actually says, how it connects to the fire code testing requirement, and what you need on file.
What section 5155 says
California Code of Regulations Title 8, section 5155 lists permissible exposure limits for airborne contaminants. Carbon monoxide has an 8 hour time weighted average limit of 25 ppm, which is stricter than the federal OSHA limit of 50 ppm. It is an occupational exposure limit: it governs what people breathe over a shift, not what a panel should be set to alarm at.
The practical consequence is that if anyone works in or regularly passes through the garage, attendants, valets, maintenance techs, delivery staff, the building has to keep CO below that average. The way an enclosed garage does that is mechanical ventilation, and the way ventilation is controlled without running 24 hours a day is CO detection.
How it connects to the fire code
The fire and building codes are what require the equipment. California Fire Code 916.11 requires gas detection systems to be inspected and tested not less than annually, with each sensor calibrated at the interval its manufacturer specifies, typically every 6 to 12 months. IBC 406.4.2 requires mechanical ventilation for enclosed parking garages, which may be operated continuously or controlled automatically by CO detection. Full detail is on our code requirements page.
So the chain is simple: 5155 sets the level, the building code requires ventilation to hold it, and the fire code requires the detection controlling that ventilation to be tested and calibrated. Skip the calibration and the whole chain stops meaning anything, because an uncalibrated sensor can read 8 ppm in a garage sitting at 60.
Alarm setpoints versus the exposure limit
Garage CO systems normally run two or three setpoints, a low level that starts the fans and a higher level that alarms and may signal the fire alarm panel. Those setpoints are set well above 25 ppm on purpose, because they respond to short spikes, not to an 8 hour average. Do not let anyone tell you a panel alarming at 100 ppm proves compliance with 5155, or that a 25 ppm setpoint is required. The two numbers answer different questions.
What documentation actually protects you
- A dated service report per sensor with the as found reading, the calibration gas concentration and the result after adjustment
- Evidence the ventilation interlock was tested, that the fans actually started when the sensor saw gas
- A record of any sensor replaced because it would no longer hold calibration
- The interval you follow and why, usually the manufacturer’s stated calibration interval
That is exactly what a proper calibration visit produces. If your last report is a line item on an HVAC invoice that says “checked CO system”, you do not have documentation.
Where garages usually fail
Sensors past their calibration interval, sensors that were calibrated but whose fan interlock was never tested, panels in a fault state nobody notices because the buzzer was silenced, and replacement sensors installed without being calibrated in place. All four look fine from the lobby and none of them survive a question from an inspector.
Getting it straightened out
We do gas monitoring only: calibration and testing, repair, retrofit and new installation. Tell us the building and roughly how many sensors are in the garage and we will tell you what it needs and what it costs.
Common questions
What is the Cal/OSHA CO limit?
Title 8 section 5155 sets permissible exposure limits for airborne contaminants, and for carbon monoxide the 8 hour time weighted average is 25 ppm. It is an exposure limit for people working in the space, not an alarm setting, but it is the number your ventilation and detection system exists to keep you under.
Does 5155 require CO detectors?
No. Section 5155 sets the exposure limit; the requirement to install gas detection in an enclosed garage and to tie it to the ventilation comes from the fire and building codes. In practice they work together: the codes require the system, 5155 is the level the system has to hold.
Who enforces which?
Cal/OSHA enforces 5155 when an employee complains or is exposed, usually parking attendants, valets, maintenance staff. Fire inspectors and building officials enforce the detection and ventilation requirements. Both end up asking for the same thing: current calibration records.
How do we show we are compliant?
Keep a dated calibration and inspection report for every sensor, showing the as found reading, the span gas used and the result. If the sensors have not been calibrated, you have no evidence the readings mean anything, which is the position nobody wants to be in during an investigation.
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.