Pollutants created by oil furnace failure

Barbara Appelbaum notes that finely divided soot particles often
don't cause objects to look "dirty" after "puff back" events.

>We have helped clean up at least three of these.  Several things
>seem to be recurring issues.  The distribution of soot obviously
>depends on the circulation of air, but it is difficult to tell
>without testing where the soot has gone because things do not *look*
>dirty. This is because the soot is so finely divided.  Because the
>things do not look dirty or damaged, and because everything within
>range of the soot including walls, floors and ceilings still needs
>complete cleaning, it may be difficult to get insurance to pay the
>full cost.

Recent research suggests that while soiling may not be visible up to
a certain threshold level for the standard observer, the overall
magnitude of soot deposition may be heavily underestimated when
based upon earlier findings.

Caltech and the GCI studied the soiling effects of particulate soot
in the early 90's. At that time the best data on the subject of
perceptible soiling was the research of Carey (1959), and confirmed
by Hancock et al. (1976). They agreed that a coverage of 0.2% on a
white surface constituted this threshold. Nazaroff and Cass used
this value to calculate a time for "just perceptible soiling" using
Nazaroff's particle deposition model. The deposition model was
validated in several Southern California museums and is reliable.
What may not have been reliable was the earlier work of Carey and
Hancock.

Recently, Bellan, Cass and Salmon reevaluated perceptible soiling
using superior techniques for creating test panels on white and a
series of characterized Munsell colors used as backgrounds.  The
earlier data appears to be off the mark by well over a factor of
ten. For dark colors the situation is even worse.

This research will be submitted to a proper conservation journal.
However, in the context of oil furnace "puffbacks" or any other
similar phenomenon, the potential for some chemically distinct
fraction of that deposition causing long-term effects on the
materials of artifacts can not be ignored in light of the far higher
loading values that now seem evident before things look "dirty".

                                  ***
                  Conservation DistList Instance 12:70
                Distributed: Thursday, February 25, 1999
                       Message Id: cdl-12-70-001
                                  ***