Another idea, on the basis of the fact that, like Roy, I found that most references to "exceeding factor", "exceedance factor" and "excess factor" occurred in translation. Searching for English-language material, I also found the term "excursion factor", where "Überschreitung" would have to be used in the sense of "Abweichung".

0.05 mg/m3 DFG MAK (peak limitation category - II, with excursion factor of 4) (inhalable dust fraction) (metal and inorganic compounds)
http://www.evidenttech.com/assets/docs/MSDS/EviComposite-Cds...

See also this document (although again originally from German):
Short-term exposure measurements. The aim of these measurements is to detect short-term increases in exposure. The excursion factor has been set at 1 for a number of chemical components of dust, i.e. the limit value must not be exceeded at any time. Numerous insoluble, non-toxic dusts and most toxic metal dusts have been assigned an excursion factor of 4.
http://www.wiley-vch.de/books/sample/3527311386_c01.pdf