ASHRAE Journal - November 2010 - 72

engineer’s notebook

What’s in Air We breathe
G
by Max sherman, Ph.D., Fellow ASHRAE

iven how long indoor air has been studied, we might think we

actually know what’s in it. Surprisingly, we have a poor idea, at

least until recently. Logue, et al., have done a hazards assessment1 of the nine most hazardous chemicals in indoor air.2
burned stuff
The Banpo villagers of central China had chimneys in their homes 7,000 years ago.3 They figured out it was not a good idea to breathe the products of combustion. Today, we still burn stuff in our homes: food, gas, candles, wood, etc. Logue, et al., identified several products of combustion that are at hazardous levels, including acrolein, benzene, butadiene, nitrogen dioxide and fine particles. Acrolein4 was at the top of the list of priority hazards. Although it’s not the stuff found in the highest concentrations, it’s very low acceptable level means it is quite often at unacceptable levels. etaldehyde to be a hazard in most homes; formaldehyde is right after acrolein on the list. Unlike acrolein, formaldehyde is a useful industrial chemical, and it is found in many household materials such as wood products, adhesives, etc. Another name for “smelly” is “aromatic,” but in chemistry that word refers to a special class of smelly compounds. Three aromatic compounds identified as priority hazards are benzene, naphthalene and paradichlorobenzene (PDB). Most of the benzene found probably comes from outside the conditioned space proper, but that is not true of the other two.

The only two chemicals that Logue, et al., found consistently hazardous in this category are our aromatic friends naphthalene and PDB. Naphthalene is the traditional “moth ball” many of us remember, but it has been phased out in favor of PDB. PDB is also in products such as toilet or urinal “freshener” blocks. Many find the PDB odor fresh and pleasing. That is not to say that other intentional poisons are not important in indoor air, but no other single chemical seems to show up broadly enough to make the hazards list.6

nasty stuff
Chlorine is in a lot of poisonous compounds. This is not surprising as it is pretty nasty stuff.7 While PDB was the only chlorine-containing compound to be found a priority hazard, there were lots of chlorine containing chemicals lower down on the list including hexachlorobutadiene, benzyl chloride, vinyl chloride, methylene chloride, tetrachlorothene, dichloropropane, tetrachloroethane, dichloroethane, trichloroethene, and, of course, chlorine. One such chemical deserves special attention as it should have been on the priority hazards list, but wasn’t: carbon tetrachloride (“carbon tet”). Fifty years ago carbon tet was a miracle chemical. It was used for dry cleaning and a host of consumer products.8 Unfortunately, it

smelly stuff
Many of the hazardous chemicals found by Logue, et al., have detectable odors at relatively low concentrations. One class of such compounds is called “aldehydes,” which typically are smelly and irritating.5 Logue, et al., found formaldehyde and ac-

Dead stuff
We like to kill stuff in our buildings even more than we like to burn stuff. We use lots of pesticides, germicides, fungicides, bactericides, herbicides, biocides, and disinfectants in our buildings. Not surprisingly, chemicals designed to kill living things are often not very good for us either.

1. Logue, J.M., T.E. McKone, M.H. Sherman, B.C. Singer. “Hazard assessment of chemical air contaminants measured in residences.” Published online in advance of print in Indoor Air at http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2010.00683.x/abstract. 2. The assessment was limited to residential environments, but I won’t let that deter me from generalizing to the whole of the indoor environment. 3. This village was discovered outside of the Imperial city of Xian. If you can get the tour bus to stop there, it is on the way to see the famous terra-cotta warriors. 4. Acrolein was used as a chemical weapon in World War I. Unlike most of the other chemical weapons, acrolein is not outlawed by the Chemical Weapons Convention (CWC). This is partly because it can be made incidentally as a product of combustion. 5. “Smelly” is not necessarily bad. Cinnamaldehyde is the odorous part of cinnamon and smells fantastic, but if you get the pure stuff on exposed skin it is like poison ivy on steroids. Don’t ask. 6. Since “no pest strips” have fallen out of favor, PDB and naphthalene are probably the only poisons that emit continuously in our homes. 7. Like acrolein, chlorine was used in WWI as a chemical weapon, which is probably why you didn’t know it was green-yellow. In fact, chlorine is the father of all the chemical weapons as it was the first one used. 8. If you have a lava lamp from the ’60s, be careful. It is probably filled with carbon tetrachloride. One of the great advances of modern chemistry has been the ability to make a non-toxic lava lamp.

ASHRAE Journal

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November 2010

ASHRAE Journal - November 2010

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