News & Information Blog

Which Limit Applies When?

By Susen Trail | 08/30/2022

I recently reviewed a report from an Indoor Air Quality study for a residential client.  What caught my eye was the Volatile Organic Chemical, Carbon monoxide, and Carbon dioxide results were compared to Occupational Exposure Limits.  There are several reasons why this is inappropriate that will be detailed in this short blog.

The first thing you learn in Toxicology is that the Dose Makes the Poison, Paracelsus 1538.  In the Victorian era it was not uncommon to eat a little Arsenic to improve the complexion.  Itinerate horse and pony salesmen would fatten up their stock as well as feed the animal arsenic to make the coat and hooves shiny.  However, after the horse was purchased, the animal would mysteriously die when the Arsenic that had accumulated in the fat tissues re-entered the blood stream.

Dose is the quantity taken into the body and it is dependent on the concentration of the contaminant, duration of exposure and frequency of exposure.  This is just one of the reasons why Occupational Exposure Limits are much larger than safe residential levels of the same contaminant.

The activity level, at work or at home, affects the volume of air, inhalation rate, and how deeply contaminated air is drawn into the lungs.  At home this can vary significantly during the day and day to day, while most work activities are repetitive. 

Here are just a few examples of the population and conditions used to develop OELs:

  1. Occupational exposure limits were first developed by the military using young, fit, men more recent research uses the ever available, and broke, graduate students. 
  1. The research, in almost all cases, was limited to 8 hours with at least 16 hours away from exposure for the body to recover.
    • Some current OELS can be adjusted for work shifts longer than 8 hours but most are not.
  1. OELs do not take into consideration off site environmental/neighborhood exposures. Such as cigarette direct or second-hand smoke, vehicle exhaust, etc.
  1. Exposures at work vary as the worker moves closer to and farther away from the exposure source.
  1. Exposure rates and sources are easily recognized and usually do not vary significantly from day to day.

Safe occupational exposure limits (OELs) are not applicable to safe residential exposure conditions.

  1. The residential population, includes people with illnesses, the elderly, children, and pets.
  1. Residents spend much more time in the home than 8 hours and much less time away from it for recovery.
  1. The proximity and duration to the source of the air contamination may vary greatly due to movement around the house and time spent outside the house.
  1. It can be much more difficult to recognize exposure to air contamination as many hazardous chemicals are odorless and colorless such as Radon and Carbon monoxide.
  1. Duration of exposure can cause different adverse health effects between people in the residence; such as when one has almost 24 hour exposure to the contaminant day after day and others have 12 or less hours at home.
  1. Individual biochemical and physiological conditions can cause sensitization in one family member causing severe adverse health effects while no one else in the family has any.

Sometimes safe residential exposure levels are hard to find.  If you carefully word your internet search you can find them for VOCs as a group, Carbon monoxide, Relative Humidity and Carbon dioxide in American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) documents or the Environmental Protection Agency website, although, their focus is the environment, as in outside your home.  However, the EPA is paid by citizens so their information is free while ASHRAE research is funded by members and sales of its researched data, so you may have to pay but the data tends to be more appropriate.

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