[Code of Federal Regulations]
[Title 40, Volume 18]
[Revised as of July 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR92.110]

[Page 427-428]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 92--CONTROL OF AIR POLLUTION FROM LOCOMOTIVES AND LOCOMOTIVE ENGINES--
Table of Contents
 
                       Subpart B--Test Procedures
 
Sec. 92.110  Weighing chamber and micro-balance.

    (a) Ambient conditions--(1) Temperature. The temperature of the 
chamber (or room) in which the particulate filters are conditioned and 
weighed shall be maintained at a measured temperature between 19  deg.C 
and 25  deg.C during all filter conditioning and weighing.
    (2) Humidity. The relative humidity of the chamber (or room) in 
which the particulate filters are conditioned and weighed shall be 
458 percent during all filter conditioning and weighing. The 
dew point shall be 6.4 to 12.4  deg.C.
    (b) Weighing balance specifications. The microbalance used to 
determine the weights of all filters shall have a precision (standard 
deviation) of no more than 20 micrograms and readability down to 10 
micrograms or lower.
    (c) Reference filters. The chamber (or room) environment shall be 
free of any ambient contaminants (such as dust) that would settle on the 
particulate filters during their stabilization. It is required that at 
least two unused reference filters remain in the weighing room at all 
times in covered (to reduce dust contamination) but unsealed (to permit 
humidity exchange) petri dishes.

[[Page 428]]

    (1) These reference filters shall be placed in the same general area 
as the sample filters. These reference filters shall be weighed within 4 
hours of, but preferably at the same time as, the sample filter 
weighings.
    (2) If the average weight of the reference filters changes between 
sample filter weighings by 5.0 percent (7.5 if 
the filters are weighed in pairs) or more of the target nominal filter 
loading (the recommended nominal loading is 0.5 milligrams per 1075 
square millimeters of stain area), then all sample filters in the 
process of stabilization shall be discarded and the emissions tests 
repeated.
    (3) If the average weight of the reference filters decreases between 
sample filter weighings by more than 1.0 percent but less than 5.0 
percent of the nominal filter loading then the manufacturer or 
remanufacturer has the option of either repeating the emissions test or 
adding the average amount of weight loss to the net weight of the 
sample.
    (4) If the average weight of the reference filters increases between 
sample filter weighing by more than 1.0 percent but less than 5.0 
percent of the nominal filter loading, then the manufacturer or 
remanufacturer has the option of either repeating the emissions test or 
accepting the measured sample filter weight values.
    (5) If the average weight of the reference filters changes between 
sample filter weighings by not more than 1.0 percent, then 
the measured sample filter weights shall be used.
    (6) The reference filters shall be changed at least once a month, 
but never between clean and used weighings of a given sample filter. 
More than one set of reference filters may be used. The reference 
filters shall be the same size and material as the sample filters.