Environmental Engineering Reference
In-Depth Information
fer heat from the wick by convection. In two-stage heaters, there is a second
chamber above the radiant element that is designed to further oxidize CO
and unburned or partially burned fuel components.
Laboratory studies of both unvented gas and kerosene space heaters
indicate that they have the potential to emit significant quantities of CO
,
2
, and aldehydes into indoor spaces. Based on the
chemistry of combustion, they would also be expected to emit large quan-
tities of water vapor. Emission potentials depend on heater type, operating
and maintenance parameters, and the type of fuel (relative to SO
CO, NO, NO
, RSP, SO
2
2
emissions)
used. Radiant heaters produce CO at rates twice those of convection heaters
and about 3 times those of two-stage heaters. Convection heaters have sig-
nificantly higher emissions of NO and NO
2
compared to both radiant and
two-stage heaters. Decreasing the wick height, a practice homeowners
employ to decrease fuel usage, results in increased emissions of CO, NO
2
,
and formaldehyde (HCHO). Maltuned heaters have significantly higher
emissions of CO and HCHO (as much as 20- to 30-fold). Emissions of SO
2
2
depend on the sulfur content of kerosene. Grade No. 1-K kerosene has a
sulfur content of 0.04% by weight; grade No. 2-K may have a sulfur content
as high as 0.30%. The latter has been more widely used than the former.
A variety of laboratory studies have been conducted to predict human
exposures, and a few have attempted to measure contaminant levels in
indoor spaces during heater operation. In one laboratory chamber study
designed to simulate heater operation in a moderate-sized bedroom with an
air exchange rate of one air change per hour (1 ACH), very high contaminant
exposures were predicted (SO
levels >1 ppmv; NO
levels in the range of
2
2
in the range of 0.1 to
1%). Potential exposure concentrations under different ventilation conditions
are illustrated in
Figure 3.2
for radiant and convective kerosene heaters.
Reference is also made in this figure to the National Ambient Air Quality
Standards (NAAQS), Occupational Safety and Health Administration
(OSHA) standards, and guidelines once recommended by the American Soci-
ety of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
Unvented kerosene and gas-fueled space heaters have been used by
homeowners and apartment dwellers under varying conditions of home air
space volumes, ventilation rates, number of heaters used, and daily and
seasonal hours of operation. As a consequence, exposure concentrations vary
widely. In a study of 100 U.S. houses, NO
0.5 to 5 ppmv; CO in the range of 5 to 50 ppmv; CO
2
levels in homes operating one
kerosene heater averaged ~20 ppbv; with two heaters, 37 ppbv; in control
homes, NO
2
concentrations averaged ~4 ppbv. Over 49% of the residences
had concentrations of NO
2
>50 ppbv during heater use, with approximately
8% exceeding 255 ppbv. Over 20% had average SO
2
levels >0.24 ppmv, the
24-hour ambient air quality standard. In other studies, carbon monoxide was
reported in the range of 1 to 5 ppmv; there were also significant increases
in RSP, in the range of 10 to 88
2
.
Kerosene heater usage has declined substantially from its peak in the
mid-1980s. As a consequence, the number of individuals exposed has also
ยต
g/m
3
