Indoor Air Quality and the four Ps (Part I)

Whenever we are dealing with building occupant complaints and adverse health effects, it is important to remember that there are series of links in the chain of causation. For Indoor Air Quality (IAQ) problems that are caused by exposure to some sort of airborne contaminant(s), the chain of causation can be boiled down to a fairly simple (at least on paper) equation:

Pol + Path + Pres + Peo = Prob


Pol = Pollutants

Path = Pathways

Pres  = Pressures

Peo = People

Prob = Problems

There’s really not all that much to it, but once when you understand the principal and the mechanisms behind it, then you can usually resolve many of the possible problems.


Pollutants come in a variety of forms.  There can be particulate pollutants, such as diesel fumes, pollen, or smoke; vapor pollutants, such as formaldehyde and other volatile organic compounds from laminate flooring, furnishings or paints; or gaseous pollutants, such as carbon monoxide or nitrogen oxides from combustion sources.  They can come from man-made sources, such as exhaust from laboratory fume hoods or kitchen exhausts; or from natural processes, such as smoke from wild fires or microbial growth as a result of water intrusion.

Sources of pollutants can be from either outside the building, such as soil gas or exhausts from vehicles and nearby buildings; or from within the building, such as emissions from copier machines, use of cleaning products, or from the occupants themselves (e.g., perfume, body odors, cooking, etc.).  Often, the pollutant source causing the problem can be determined by finding and identifying the pathway that it is using to reach the affected individuals.


Buildings usually have numerous different pathways through which pollutants can migrate.  Air handling systems can draw in pollutants through the outdoor air intakes, or via the return air ducting, and then distribute them throughout the building.  Stairwells, elevator shafts, utility shafts, conduits and other penetrations, both between floors and in the building envelope, all can act as pathways for pollutants.  The movement of people through a building, and their actions, can have a large impact on the movement of pollutants as pathways can be created and changed as doors and windows are opened or closed.

Even small holes or cracks in walls and foundations can allow significant amounts of air through them if there is a big enough pressure differential from one side to the other.   I once had a situation where the occupants on one floor of an office building in midtown Manhattan were complaining about intermittent cigarette and marijuana smoke odors.  The building shared a common masonry “exterior” wall with an adjacent Broadway theater.

When we investigated further, it turned out that, on the other side of that common wall, there was a break room for the ushers and that the ushers liked to relax with a smoke or two during their downtime.  Although there were no obvious penetrations in the common wall, it was clear that smoke and odors from the usher’s break room were being drawn from that space, and into the adjacent office building, due to pressure differentials.