||Standard Reference Calibration for Explosion Detectors
ASTM F 2069, Standard Practice for Evaluation of Explosives Vapor Detectors,
establishes a method for characterizing explosives vapor detectors
in the laboratory. It was developed through the efforts of manufacturers,
users, and engineers in ASTM Subcommittee F12.60 on Controlled
Access Security, Search, and Screening Equipment, part of Committee
F12 on Security Systems and Equipment.
A standard was needed because users and manufacturers were making
performance claims based on different methods of calibration and
evaluation. Manufacturers were comparing apples and oranges and
the ultimate user was confused by the different performance claims,
said John R. Hobbs, Ph.D., physical chemist, Hobbs Consulting,
This standard practice requires comparisons of performance to
an accepted reference calibration and results in performance specifications
on a level playing field.
Hobbs led the working group of manufacturers and users of explosives
detection equipment, and engineers from X-ray and metal-detector
companies that developed F 2069.
This standard practice provides manufacturers with the procedures
to relate the performance of their detectors to criteria that
the ultimate users can use to determine if a particular explosives
vapor detector satisfies their requirements, he explained. Previously,
manufacturers claimed lower limits of detection based on noise,
minimum detectable level, or lowest sensitivity. These claims
did not tell a prospective user how this machine would perform
in his operational system.
This standard provides a probability of detection at a determined
minimum- alarm level and the false-alarm rate related to the performance
at that minimum-alarm level. With this information, the prospective
user can decide if the performance of a particular detector meets
his detection and false-alarm requirements for his particular
According to Hobbs, F 2069 requires the comparison of a manufacturers
secondary calibration unit to one of three acceptable primary
standards. Only manufacturers and builders of the calibration
equipment have the facilities or expertise to carry out this comparison.
The users are not equipped to do this. When manufacturers report
performance information in their product literature according
to F 2069, the user can make intelligent choices, he said.
This standard will benefit users because if the standard is followed,
the manufacturers report a probability of detection at a minimum
alarm level and an attendant false alarm rate, Hobbs affirmed.
They now can choose a detector with a higher probability of detection,
but with a higher false-alarm rate or choose one with a lower
probability of detection and a lower false-alarm rate. The user
can now trade off performance with detection probability, false-alarm
rate, and cost. Previously, manufacturers exposed real high sensitivity
without a false-alarm rate, and the user had no way to determine
if the detector would meet his requirements.
For instance, a detector with a real low limit of detection and
a false alarm rate of 20 percent may not be as good as a detector
with somewhat higher limit of detection, but with a false alarm
rate of only two percent, he concluded. The user can decide
if he needs the lower limit of detection or the lower false alarm
rate, since both of these affect the cost of performing security.
F 2069 provides a method for evaluating 11 parameters, including
interference equivalent, temperature and humidity effects, sample
and response times, overload level, etc.
For further technical information, contact John R. Hobbs, Ph.D., Hobbs Consulting, Boxford, Mass. (phone: 978/887-6082).
Individuals are welcomed to attend the next Committee F12 meeting,
Oct. 23-24, in Dallas, Texas. For details, contact staff manager
Jim Olshefsky, ASTM (phone: 610/832-9714). //
Copyright 2001, ASTM