STACK SAMPLING 1115
Test Method 21Test Method 21 is used for determining Volatile Organic
Compound (VOC) leaks from process equipment. The method
actually presents three different ways for determining leaks.
The first and most common way is to place the nozzle of a
portable instrument right against the potential leak source.
If the instrument reads above an arbitrarily defined value, a
leak is found. The second way is for screening prior for con-
ducting a survey with the portable instrument. This screening
is performed by spreading a soap solution on the flange, for
example, and looking for bubbles. The third way to look for
leaks is to look for the absence of leaks. This is performed
by measuring background concentration in the vicinity of
the process equipment with the portable instrument and then
determining whether the concentration at the equipment is
significantly higher than background. The choice of proce-
dure is dictated entirely by the prevailing regulation.
The second factor dictated by the applicable regulation
is the definition of a leak. Method 21 defines all characteris-
tics of a leak but one. As stated above, Method 21 procedures
determine that a piece of equipment is leaking when the
instrument is placed against it and reads above an arbitrarily
defined value. The regulation must supply the value. Typical
levels are 10,000 ppmv or 25,000 ppmv. The definition of no
detectable emission is then defined as a reading less than 5%
of the leak value above background. Thus, if background is
500 ppmv and the leak definition is 25000 ppmv, no detect-
able emission is reported at less than 0.05 25000 500
1750 ppmv.
Method 21 contains detailed specifications for the selec-
tion calibration, and operation of the instrument, without
specifying the detector. Flame ionization detectors and pho-
toionization detectors are the most common, but others, such
as infrared absorption, have also worked successfully for this
purpose. One of the most important criteria for selecting an
instrument is its ability to detect the compounds of interest at
the necessary concentration levels.
In order to allow consistent instrument selection and
calibration, a single compound is generally specified in
the regulation as the reference compound. All calibrations
and instrument checks are then performed using calibration
gases that are mixtures of that compound in air. A two point
calibration is performed, using zero air, at one end, and a
concentration close to the leak definition at the other.
Method 21 also contains detailed instructions for con-
ducting leak detection surveys, describing acceptable pro-
cedures for measuring leaks at various types of equipment.
These surveys may be conducted by personnel who have
been trained to do so but who may not know the details of
instrument troubleshooting, etc. However, someone at each
facility performing the survey should be qualified to work on
the instruments.Test Method 22Test Method 22 is used for determining fugitive emissions
and smoke emissions from flares. Like Method 9, it is avisual method performed by trained observers. However, this
method is not a quantitative method. This method involves
only the timing of the observed emission and the calculation
of the fraction of time that the emission is observed.
Fugitive emissions include all emissions that are not
emitted directly from a stack or duct. They include emissions
from doors, windows, cracks or holes as well as emissions
from piles or directly from process equipment or operations.
In order to perform valid readings, the observer finds a
suitable location more than 15 feet from the source, starts
a stopwatch to record elapsed observation time, and begins
observing the source. The observer continuously observes the
source, starting a second stopwatch when emissions are noted,
stopping it when they stop. This process continues until either
the regulatory requirement has been met or 15 to 20 minutes
have elapsed. At that point, the observer must take a 5 to 10
minute break. The clock time of all observations and the time
and duration of emission observation should be recorded on
an appropriate form, along with a suitable description and
drawing of the observation position, etc.
Observers need not pass the certification exam of Method 9
but must have training equivalent to the classroom part of
Method 9 certification.Test Method 24Test Method 24 is not a stack test method. Instead, it is used
to determine the amount of volatile organic solvent used to
determine the amount of volatile organic solvent water con-
tent, density, volume of solids, and weight of solids of sur-
face coatings. This method applies to paints varnish, lacquer,
and other related coatings. American Society of Testing
Methods (ASTM) procedures have been incorporated by
reference into this test method.Test Method 24ATest Method 24A is not a stack test method. Instead, it is
used to determine the volatile organic content (VOC) and
density of printing inks and related coatings.
The amount of VOC is determined by measuring the
weight loss of a one to three gram sample heated to 120
2°C at an absolute pressure of 510 51 mm Hg for 4 hours
or heated in a forced draft oven at atmospheric pressure for
24 hours. The coating density and solvent density are deter-
mined using ASTM D 1475–60, which is incorporated to
this method by reference.
The EPA Test Method 24A write-up and the ASTM method
contain detailed instructions for sample preparation and analy-
sis. These should be read before attempting this method.Test Method 25This method is used to determine the emissions of total gas-
eous non-methane organics (TGNMOs) as carbon. It is used
mainly for testing sources such as combustion sources for
which the organic constituents of the emission are unknown
and/or complex. The collected sample is injected onto a gasC019_003_r03.indd 1115C019_003_r03.indd 1115 11/18/2005 11:07:17 AM11/18/2005 11:07:17 AM