Using Triggers to Avoid IAQ Problems
General Guidelines for Responding to Abnormal Conditions
Suppose you got a call from one of your techs: “We detected some carbon monoxide in the air in the Office Bay. What do you think we should do?” You ask a few questions, and you learn that the CO concentration was measured at about 5 ppm and the outdoor air ventilation rate was running around 5 cfm/person. You tell the tech you’ll get back to him. What do these measurements mean? Is someone in danger? What is the upper acceptable limit for carbon monoxide in office spaces? And what about the fresh air ventilation rate? FROM TYPICAL TO TRIGGER There are few national or mandatory limits, codes, or regulations for airborne concentrations of IAQ contaminants. Certainly the PEL and TLV values are never to be exceeded, but those are primarily intended for industrial environments. Over the years, a number of IAQ-related guidelines and recommended limits have been suggested by ASHRAE, EPA, NIOSH, AIHA, OSHA, individual States, and the WHO. For carbon monoxide, WHO, NAAQS, and ASHRAE have suggested IAQ guidelines for upper limits ranging from 6 to10 ppm.
So, at what concentration of carbon monoxide should we be concerned and take action? After all, almost all chemicals can be found in ambient air at very low concentrations. Carbon monoxide is actually exhaled in human breath at concentrations of 0.5–2 ppm in non-smokers and 10–20 ppm in those who are smoking. So if the OA ventilation is very low, even the occupants of a space could be the source of small elevated levels of CO.
Over the years, I have compiled data related to “typical” conditions, “trigger” conditions, and “upper limit” conditions that have been suggested by various associations, agencies, and others. Table 1 presents some of these data as a checklist.

D. JEFF BURTON is an IH engineer with broad experience in ventilation used for emission and exposure control. He is author of many books, distance-learning and on-site training courses and current chair of the ANSI Z9.2 and Z9.10 subcommittees. His full bio is online and he can be contacted at Send feedback on this article to
Table 1. Typical and Trigger IAQ Parameters Checklist Caution: For general guidance purposes only; do not use for design. Always obtain competent assistance. Derived from Checklist 8 in The IAQ and HVAC Workbook by D. Jeff Burton.
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