C. M256 Kit MaintenanceMaintenance of the M256 kit is a straightforward process in which no individual part ever needs adjustment or calibration. In addition to ensuring that the carrying case is not damaged and the shoulder/waist strap is not torn or frayed, M256 kit maintenance consists of the following actions: 1) ensure that each kit contains 12 vapor-samplers, one book of M8 detection paper, and one set of instruction cards; 2) check each vapor samplers discard date (expiration date) to ensure that the date has not passed or is about to pass; and 3) ensure that each vapor-samplers protective envelope is intact. An M256 kit that contains four or fewer vapor-samplers can be replaced or combined with another kit having fewer than four vapor-samplers. When M256 kits are combined, users should observe the discard date (expiration date) on each vapor-samplers envelope. If a vapor-samplers discard date has passed (Figure 17), it must be replaced. The vapor-sampler should also be replaced if its protective envelope has been opened.
Figure 17. Carrying case discard date statement (top) and vapor-sampler discard date (bottom)
Before using a vapor-sampler, the operator must ensure that the glass reagent ampoules, test spots, or the channels connecting them are not crushed, damaged, or missing. Before conducting a chemical agent test, operators must also check the blood agent test spot for the presence of any pink colored stain. If any one of these conditions exist, the operator should get another vapor-sampler or M256 kit.
V. FALSE DETECTIONS
While the M256 kit is described as a miniature chemistry set, conducting a test on the battlefield is far different than conducting a test in a controlled laboratory. Consequently, the possibility that a substance found on the battlefield could cause the M256 kit to produce false detections must be considered.
Although the M256 kit is an improvement over older generation CWA detection kits, the M256 kit can produce false detections. False detections are of two types, positive and negative, with each having a vastly different outcome. A false positive detection occurs when the detector falsely indicates the presence of a CWA. False positive detections are considered an irritant or nuisance because they cause the extended and unnecessary wearing of the complete chemical protection suit, but do not lead to exposure to a CWA. A false negative detection, on the other hand, occurs when the detector falsely indicates that no chemical agent is present, when in fact it is present at or above the detectors minimum detection level, possibly at a casualty producing concentration level. A false negative detection is serious because it can cause individuals to prematurely take off their mask and gloves, and thereby expose themselves to a CWA.During the M256 development program, various prototype vapor-samplers underwent testing to identify substances that would produce false negative and false positive detections. During the testing, the M256 was exposed to vapors from chemical mixtures and compounds that could be found on a battlefield. The test results showed that none of the tested substances caused a false negative detection. However, several of the substances produced false positive detections. Specifically, smoke from burning brush, pyrotechnic smoke (HC), and dry supertropical bleach were found to produce false positive detections with some regularity. Results of the battlefield interference tests are contained in the following tables. Table 4 lists the interferent element, the M256 vapor-sampler exposure test, and the test result. Table 5 lists the significant contaminants which caused false positive results (identified in table 4), shows the CWA that was falsely detected, the proportion of false responses to the number of tests, and the total proportion of false positive responses. Unfortunately, neither the M256 kit operator's manual nor the Gulf War era chemical defense manuals clearly state the potential for false positive readings.
Table 4. M256 vapor-sampler battlefield interference test results