Sampling in the face of variability

The concentrations of IAQ contaminants almost always fluctuate over time.  Therefore is it best to log data over time, whenever possible.  Technology, and more importantly, budget constraints may prevent us from logging data over time.  That means we must show up on a given day and measure that point in time.  This method gives us a random reading from a normal day.

If we only have one shot at taking a measurement, some advocate aggressive sampling to simulate the absolute worst case maximum scenario.  Let me give you some examples of trying to simulate the worst case maximum scenario:

Assessments mold

Federal Agency’s Checklist for Mold

The National Institute for Occupational Safety and Health (NIOSH) is conducting a pilot study to establish a standardized checklist for a mold and moisture inspection. This checklist is more designed for building owners and operators rather than for experienced consultants. First let me explain the background of the checklist and how it works, then I’ll later provide some commentary.

Ju-Hyeong Park and Michelle Martin at NIOSH are the developers of this checklist. The pilot project was unveiled at the Federal Interagency Committee on Indoor Air Quality (CIAQ) on October 13, 2010 in Washington DC. The information in this blog post is based on that presentation.


What’s Normal vs. What’s Safe

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.


Yesterday’s Home Health Assessment

Allergy Skin Testing

Yesterday I performed a home health assessment for a woman who was referred to me by her allergist.  The woman had her fair share of allergies: dust mites, ragweed, mold and various plant and grass pollens.  But beyond the typical allergy symptoms, the woman was experiencing tightness in her chest and difficulty breathing.  Lung function tests performed by the doctor indicated that she does not have asthma.  The breathing difficulties go away when the homeowner spends more than a few hours away from the home.

In today’s blog post, I want to describe how I personally go about assessing potential indoor air quality problems like these.

The first step is to