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Understanding Carbon Monoxide (CO) Detection Systems

All kinds of gas detection requirements are being made into law by federal, state, and local governments, for public safety reasons.  The business of gas detection is booming!

One of these gases is carbon monoxide (CO).  CO is a toxic, dangerous gas.  Over time, breathing air with concentrations as low as 35 to 40 parts per million (ppm) of CO can cause headaches and nausea.  Concentrations of 300 ppm can kill!  Consequently, lawmakers have written, and are continuing to write, codes regarding CO gas, covering areas where the public could be adversely affected by concentrations of CO gas.  The focus has been on parking garages at shopping malls, hotels, apartment buildings, etc.  These are the most obvious areas where there are high concentrations of CO gas.

These codes are constantly being revised.  The codes that will be referenced in this Info-Tec are current as of this date.  Codes can be, and probably will be, changed.

As an example, OSHA administers the federal code.  The OSHA code prior to January 1, 1998, required that automatic systems maintain a level of no more than 35 ppm of CO, averaged over an eight-hour period.  Brief high levels of CO were allowed during that eight-hour period.

As of January 1, 1998, the OSHA code was revised and now states that automatic systems “maintain a level of no more than 50 ppm of CO averaged over an eight-hour period.”  No mention is made of “brief high levels.”

There are UL Standards (UL2034) and a Uniform Building Code (UBC) regarding CO detection systems, but these are almost always superceded by more stringent State or Local codes.

Since Climatic Control Company presently has branches in Illinois, Minnesota, and Wisconsin; we will concern ourselves only with the codes for these states, and only for commercial CO detectors. 

Chicago, Illinois has recently passed a local code requiring a CO detector in every residence, not just in public buildings.  Like Chicago, many municipalities are considering enacting a residential code that would require CO detectors in every home.  Like the smoke detector business, this results in the market being polluted by cheap detectors strictly for residential use.  Therefore, we will not concern ourselves with this market, except to note that Macurco does make the CM-11 for residential applications. For parking garage CO systems, the State of Illinois code is the same as the current OSHA code.  Always check with the local building inspector to find out if there are any local codes that supercede the State code, especially in Illinois.

The State of Minnesota code follows OSHA code recommendations concerning ppm, but also requires “one CO detector for every 5000 square feet,” and the CO detectors must “fail safe.”  That is, if a malfunction of a detector occurs, the fan relay must react as if an activating CO level has been detected.  Macurco detectors are fail safe, and as of this date, they are the only fail safe detectors on the market.  Minnesota’s inspectors are aware of this, and automatically approve systems using Macurco detectors.  If other manufacturers’ detectors are used, they will require those systems to incorporate a timer to run the exhaust ventilating fans 15 minutes out of every hour.  This could be a big energy waster, especially if the garage is heated.

As of April 1, 1997, the State of Wisconsin code for automated systems is: “The system shall be activated to provide exhaust ventilation rates as specified in ILHR64.05 by a continuous monitoring and detection system which can maintain CO levels below 35 ppm and nitrogen dioxide levels below 1 ppm.”

Note the addition of the NO2 detection requirement.  Prior to April 1, 1997, NO2 detection was not required in Wisconsin.  There was no “grandfathering” of systems.  Systems that were installed without NO2 detection do not meet code!  If you are aware of any CO detection systems installed in Wisconsin prior to April 1, 1997, they probably don’t have N02 detectors.  To bring them up to code, the NO2 detectors must be added.  These detectors were made part of the Wisconsin code because they react to diesel exhaust.  The only NO2 detector on the market, as of this date, that can detect 1ppm nitrogen dioxide as required by Wisconsin code is the Macurco ND-1.  (Please refer to the attached specification and installation sheets on the ND-1 nitrogen dioxide detector and controller.)

There are not enough inspectors to inspect every CO detection system on every previously built commercial building in the State of Wisconsin.  Consequently, most building owners are not aware that their systems do not meet code.  They are most commonly informed of non-code compliance when the building is being sold to a new owner.  Inspection is made before a buyer takes title, and the seller must bring the building up to code before the sale can be completed.  Even if an owner does not intend to sell, he is taking on the liability of non-code compliance and the possibility of a huge loss in today’s litigious society.

In every state Climatic Control Company operates in, the Macurco CM-21A is a good device for a low-cost CO detector.  Study the attached specification and installation sheets for the CM-21A.

Note that the CM-21A is checking itself and the CO level every 2.5 minutes.  It averages the CO level in ppm over 5 minutes, or two cycles, for fan relay activation.  As an example, should the first CO sample be 50 ppm, and 2-1/2 minutes later the sample be 10 ppm, the 5-minute average would be 30 ppm and no action would take place.  However, if the first sample were 50 ppm and the second sampling 20-ppm, the average would be 35 ppm and the SPDT fan relay would be activated.

If the CO level averages 100 ppm to 199 ppm for 30 minutes, the alarm relay is activated.  Of course, the fan relay has already been activated.  Should the CO level ever get to 200 ppm or more, averaged in 10 minutes, the alarm relay is activated.  Again, the fan relay has already been activated.  The 2.5 minute cycle allows for high level spikes of CO to clear before setting off any alarm or turning on the fans, as when a poorly-tuned car would pass close to a detector, raising the CO level momentarily to 35 ppm.  Once activated, the fan or alarm relays will stay activated for a minimum of 2.5 minutes, even if the CO level drops below 35 ppm.

The CM-21A detects only the dangerous toxic CO gas.  It will not react to gasoline, oil, or other fumes or gasses, thereby avoiding false alarms.

There are no adjustments to make when installing the CM-21A.  Everything is factory set.

Neither the CM21A nor the ND-1 contains any audible alarm.  As shown in the wiring diagrams, they must be connected to an alarm device.  The ND-1 has a display, which can notify the user on the ppm readings of CO as well as system error diagnostic readouts.  See Figure 1 for the error code descriptions.

Figure 1.

There are usually no definite, precise specifications on detector location.  Air circulation, layout, partitions, and air inlets are factors that must be considered, as they vary from building to building.  The area covered by a single detector can vary greatly.

If there are no restrictive partitions in a building, the Minnesota code requirement of one detector for every 5000 square feet is a good rule to follow.

CO is slightly heavier than air, so one would expect it to concentrate near the floor, but this is true only in “dead” air.  Natural air circulation, with people and cars moving around, will normally cause the dispersal of CO so the concentration will be about the same within the monitored spaces.  Detectors should be mounted about five feet above the floor where the average person breathes.  Do not put detectors in corners or directly in front of any air inlet.  Doors, windows, and ramps can be considered air inlets.

These general guidelines should be used only if no specific installation codes exist.  As mentioned earlier, codes are being updated constantly.  It cannot be over-emphasized that you ALWAYS check with the local building inspector for any codes regarding CO systems.

Data Sheets For CM-21A:

Data Sheets For ND-1:

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