To:	Jeff Telander						From:	Dave Reeves 

Project File						Date:	March 17, 2008

Re:	Mineral Wool Production – Acute Exposure Factor

When the initial acute health risk screening was performed, EPA used
conservative assumptions for emission rates, meteorology, and exposure
location.  The following worst-case assumptions were used in the
screening approach:

•	Peak 1-hour emissions were assumed to equal 10 times the average
1-hour emission rates.

•	For facilities with multiple emission points, peak 1-hour emissions
were assumed to occur at all emission points at the same time.

•	For facilities with multiple emission points, 1-hour concentrations
at each receptor were assumed to be the sum of the maximum
concentrations due to each emission point, regardless of whether those
maximum concentrations occurred during the same hour.

Based on the initial risk results, we then refined the approach to come
up with an acute exposure factor to be used in the subsequent risk
screening.  There are equipment and process limitations on how the
melting furnaces (cupolas) are operated – which limits the emissions
for a given facility.  The cupolas are considered batch operations, but
are run on a continuous or semi-continuous basis to save time and energy
to heat up the furnace for each batch.  Fiber collection, including the
application of the binder, curing, and cooling are not performed
intermittently during the course of a manufacturing campaign without the
loss of materials or product; therefore, these formaldehyde-emitting
processes in bonded mineral wool fiber manufacturing are continuous
processes with minimal fluctuation and not subject to large short-term
spikes in emission rates. 

Discussions with industry experts indicated that the continuous nature
of the process would not lead to large fluctuations in the hourly
emission rates, and that a more reasonable, yet still conservative,
ratio of peak-to-mean hourly emission rate is 2, rather than 10 (see
NAIMA comments dated June 29, 2007 on ANPRM – Docket ID No.
EPA-HQ-OAR-2006-0859).   Raw material feed rates in mineral wool
processes are essentially constant with minimal fluctuation
(approximately ± 10 percent).  Consequently, emissions also have
minimal fluctuation. In refining the acute risk assessment, a short-term
emissions multiplier of 2 was used to estimate the maximum hazard from
acute exposures, with 1.5 of the factor accounting for two daily shifts,
and 0.5 of the factor accounting for up to 33% emissions variability in
the processes.

