CO/NO2 in parking garage - Florida

[Michael Brown]

The IMC allows for intermittent control of a parking garage ventilation system if a CO/NO2 system is installed. Florida amended that code section to specify that the NO2 sensor be mounted 12 inches below the ceiling. This amendment favors a specific manufacturer who's installation instructions recommend the same location. Other manufacturer's specify that the NO2 sensor be installed in the breathing zone. The code also states that the sensors shold be installed in accordance with the manufacturer's instructions but in this case, that would not comply with the location specified in the code. Which part of the code takes precedence, the specified location or the manufacturer's instructions?

 

[e hilton]

What height is the breathing zone, where the other brands recommend installation? Does CO/NO2 rise or fall?

 

[steveray]

This is what I was thinking (IMC)....But it doesn't say what I want it to for this application ? I don't think.....But maybe it does?

304.2 Conflicts. Where conflicts between this code and the
conditions of listing or the manufacturer’s installation
instructions occur, the provisions of this code shall apply.
Exception: Where a code provision is less restrictive than
the conditions of the listing of the equipment or appliance
or the manufacturer’s installation instructions, the conditions
of the listing and the manufacturer’s installation
instructions shall apply.

 

[Michael Brown]

What height is the breathing zone, where the other brands recommend installation? Does CO/NO2 rise or fall?

The brand we use recommends both sensors at 60". They also make a combo sensor which detects both gases for mounting at that height. CO doesnt necessarily rise or fall and NO2 falls and tends to collect in low lying spaces.

 

[Michael Brown]

This is what I was thinking (IMC)....But it doesn't say what I want it to for this application ? I don't think.....But maybe it does?

304.2 Conflicts. Where conflicts between this code and the
conditions of listing or the manufacturer’s installation
instructions occur, the provisions of this code shall apply.
Exception: Where a code provision is less restrictive than
the conditions of the listing of the equipment or appliance
or the manufacturer’s installation instructions, the conditions
of the listing and the manufacturer’s installation
instructions shall apply.

I was asked by our rep if we were having any problems in Florida becasue they had been getting push back from some juricdictions. I agree that 304.2 should allow us to follow the manufacturer's instructions but I wasnt sure if there was anything else that could tip that the other way. I dont know that the location specification would necessarily be considered a restriction unless I were to make the arguement that the placement of the NO2 sensor at 60" allows for earlier detection of that gas.

 

[mtlogcabin]

FL IMC 2020 edition​

404.1Enclosed parking garages.​

Mechanical ventilation systems for enclosed parking garages shall operate continuously or shall be automatically operated by means of carbon monoxide detectors applied in conjunction with nitrogen dioxide detectors. Carbon monoxide detectors shall be installed 3 to 5 feet above floor level and nitrogen dioxide detectors shall be installed 1 foot below ceiling level. Such detectors shall be listed in accordance with UL 2075 and installed in accordance with their listing and the manufacturers’ instructions. Automatic operation shall cycle the ventilation system between the following two modes of operation:

1. 1.Full-on at an airflow rate of not less than 0.75 cfm per square foot of the floor area served.
2. 2.Standby at an airflow rate of not less than 0.05 cfm per square foot of the floor area served.

I believe 304.2 is applicable since FL did not delete what is highlighted in red

​

Other Factors for Consideration The source of the gas can make a large difference in its anticipated location. Take for example nitrogen dioxide (NO2). Nitrogen dioxide is often found as a byproduct of burning diesel fuel. At room temperature, nitrogen dioxide is heavier than air; but when heated, as it is when being exhausted from a vehicle, it is lighter than air. This results in the hot gas first rising to the ceiling before cooling down and settling at the floor. Furthermore, some diesel vehicles exhaust from a tailpipe mounted underneath the rear bumper while others exhaust through a stack on the top of the vehicle. Although the gas is the same, the mounting height of the sensor may need to change to obtain a quicker response time. A sensor mounted at breathing height is still a safe option, but it may not be the most optimal in certain applications. The classification of gas is another very important consideration. The primary danger from toxic gases comes when they are inhaled. Thus, mounting sensors at breathing height can make a lot of sense in a variety of situations. Conversely, flammable and/or corrosive gases do not need to be in contact with humans to pose a danger. The mounting height most optimal for them is the one that will yield the quickest response time. The final key factor to pay attention to is the type of sensor being used to monitor an area. An infrared (IR) sensor relies on having line-of-sight to properly detect the presence of a gas. If there are obstructions like tables, cabinets, or vehicles in the way, the effectiveness of the sensor will be reduced. Care should be taken to mount these so they can “see” over any longterm obstructions. Other types of sensors like electrochemical or MOS sensors are less particular as they sample the air near the sensor. Still, mounting the sensor at a height where air circulation is poor will hurt its ability to accurately measure concentrations of gas