What’s Normal vs What’s Safe

Sep 10, 2010

Every office has some employees with headaches.  What number of headaches would you deem excessive? What’s normal?

Indoor air contaminants are present in every home, school and office.  But are the concentrations high enough to warrant concern?  What’s safe?

When measuring indoor air quality parameters such as carbon monoxide, VOCs, mold or allergens, you’ll be faced with interpreting the results.  Your clients want straightforward answers to two common questions, “Is this normal?” and “Is this safe?”  At first glance, these questions seem identical, but there is an important distinction I would like to highlight in this post.

“Is this normal?” looks at the concentrations found in similar building types in a similar climate zone during a similar time of year. Concentrations of contaminants are usually in flux, leaving a normal, lognormal or other distribution.  Plotting out historical data from similar buildings will typically create a bell shaped curve that can help answer the question, “Is this normal”?  When taking measurements, you may record a reading that falls a few standard deviations from the mean.  This is a good indication that the level is not normal.

A great way to establish if a level is “normal” or not, is to compare your data to that collected during the EPA BASE study.  You can get a summary of their findings on the EPA website, or order a copy of their entire database on CD for free.  I’ll describe how to leverage the EPA data more in a later post.

In the grand scheme of things, establishing what is normal is quite easy.  The more difficult question is “Is this safe?”  In other words, you can measure elevated levels of allergens in a home, but does that necessarily mean it is having an effect on occupants’ health?

Clients want to know the exact effect contaminant levels are having on occupants.  However, this becomes a slippery slope.  A consultant should never be dispensing medical advice or making a medical determination.   OSHA has permissible exposure limits (PELs) and the American Conference of Governmental Industrial Hygienists (ACGIH) has their threshold limit values (TLVs) to guide us.  But be very careful answering the question, “Is this safe?”

Therefore, as a consultant in this field, your goal should be to establish if the exposures are exceeding what is normal.  What effect these excessive levels have on human health should be left for the doctors.