What the MSDS probably means by reference to the ACT and SCAQMD Rule
1171 is that the cleaning solvent's vapor pressure is less than 10
millimeters of mercury (mm Hg) at room temperature (20 to 25 C).
According to page 6 of the June 1994 Alternative Control Techniques
Document: Offset Lithographic Printing (ACT), the South Coast Air
Quality Management District (SCAQMD), i.e. LA and Southern California,
Rule 1171 "limits the VOC composite partial vapor pressure of cleaning
materials for offset printing to 25 mm Hg at 20 degrees Celsius (C)."
In addition, the ACT says using cleaning materials with <10 mm Hg at 20
C vapor pressure "would result in a comparable emission reduction to
using cleaning materials that contain less than 30 weight percent VOC."
EPA Method 24 gives you the official VOC content. For doing emission
inventories, find out from the state or local air quality authority what
emission factor they will accept for your equipment and cleaning solvent
vapor pressure. According to the ACT page 7, "for cleaning materials
with a VOC composite vapor pressure less than 10 mm Hg at 20 C about 50%
of the VOC may remain on the towel after use." An emission factor of
50% seems reasonable, unless a shop can demonstrate better solvent
recovery from centrifuges, etc. In Lincoln, printers usually multiply
the manual blanket wash (vapor pressure typically 2 to 6 mm Hg)
throughput by the Method 24 VOC content (typically 100%) by an emission
factor of 50% to estimate emissions for the inventory.
Automatic blanket washes with <5% VOC content by EPA Method 24 (and
usually <1 mm Hg vapor pressure) are being used fairly often now. See
the printech archives for details.
> Is anyone familiar with this product, Ultimate Solvent Alternative
> (USA) Wash from Nensco? The MSDS lists the VOC content as 55.6% by
> weight using EPA method 24, but then says its 0% by weight as per
> EPA's ACT for Offset Lithographic Printing, and 0% according to
> California's SCAQMD Rule 1171. What is the right VOC content? Which
> one can I use on air emission logs? Any help would be appreciated.