ASHRAE Journal - November 2019 - 73

COLUMN BUILDING SCIENCES

PHOTO 3 Candles. Problems with candles, especially the scented/aromatic ones.
Ah, ambience and decoration.

* "Filter out" in carpets;
* "Plate out" on charged surfaces due to electrostatic
attraction;
* "Plate out" on cold surfaces due to "Brownian motion"; and
* "Plate out" on surfaces due to impaction.
All of these mechanisms require really tiny particles-
particles that can become aerosolized or lofted into the
air and remain airborne for many minutes or hours.
Big particles are not related to the problems observed.
Big particles fall out of the air too fast. Their movement
and distribution are dominated by gravity rather than
airﬂow, electrostatics or molecular movement such as
Brownian motion. The particle sources for the types
of really tiny particles that can cause the problems
observed are many:
* Tobacco smoke, cannabis smoke;
* Candle soot;
* Fireplace smoke;
* Soot from standing pilot lights on gas ﬁreplaces
(Photo 5);
* Carpet ﬁber pyrolysis on hot heat exchange surfaces
such as electric resistance baseboard heaters and resistance heating elements in heat pumps;
* Blown insulation pyrolysis on hot heat exchange
surfaces such as electric resistance baseboard heaters
and resistance heating elements in heat pumps; and
* Aerosolized clay, concrete cutting particulates and
gypsum sanding.
Aside from really tiny dirt, concrete cutting and gypsum sanding most of these sources have something in
common: something has to get burned, cooked, fried
or pyrolyzed in order to create the size of particles

PHOTO 4 Environmental Chamber Test. Who would have thought that candles could

cause so much damage and generate so much soot? A wonderful "benchtop"
experiment by an old school engineer shows the amount of soot from a 30-minute
candle burn.

PHOTO 5 Backdrafting Gas Fireplace. Soot from standing pilot lights on gas
fireplaces are a big source of particulates. When the full burners are on, venting
occurs. When only the pilot light is on, backdrafting is common.

required. There are a few other potential sources of
particles that could provide them in the size range necessary. However, we typically dismiss them as not likely
for obvious reasons: particles from industrial grinding
or cutting operations, fumes from welding and carbon
black from copiers or laser printers. Of course, it is possible that someone has unusual habits we don't know
about or an unusual lifestyle that we don't notice. Just
the same we don't typically notice any welding or industrial grinding going on inside the typical unit. We also
don't often notice a Kinko's-like business in most units.
Ongoing renovations to interior gypsum surfaces do
happen on occasion.
Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation in
Westford, Mass. Visit www.buildingscience.com.
N O V E M B E R 2 0 19

ashrae.org

ASHRAE JOURNAL

http://www.buildingscience.com http://www.ashrae.org

ASHRAE Journal - November 2019

Table of Contents for the Digital Edition of ASHRAE Journal - November 2019