Impact of Revised Airborne Exposure Limits on Non-Stockpile Chemical Materiel Program Activities (2005) / Chapter Skim
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4 Air Monitoring Systems
4 Air Monitoring Systems
Pages 43-61
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From page 43... ...
airborne exposure limits (AELs) levels is not typically done at non-stockpile sites because and the immediately dangerous to life and health (IDLH)
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From page 44... ...
2.00 AEL (as presented in the latest version of the Program MINICAMS provides a more rapid warning, but there is matic Laboratory and Monitoring Quality Assurance Plan generally a greater risk of false positives (for MINICAMS (U.S.
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From page 45... ...
in the phosphorusinlet of the MINICAMS during successive instrument specific mode. Also, two kinds of organophosphorus comcycles -- specifically, microliter volumes of a dilute solution pounds can cause false positives in the phosphorus-specific of agent are injected.
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From page 46... ...
The that if a MINICAMS reports an agent concentration greater PFPD, however, is still susceptible to false positives caused than the P&A study range, there is confidence that the true by organophosphorus compounds and to false negatives concentration of agent is greater than 1.50 AEL. Thus, (quenching)
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From page 47... ...
The IDLH concentration range used in the past when certifying MINICAMS, 0.20 to 1.50, and the concentration range required in the future, 0.50 to 2.00, are represented by range bars on the diamonds; (5) The CDC's 1988 TWA AEL and the CDC's 2003 15-minute STEL for GB (numerically equivalent to the 1988 TWA AEL)
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From page 48... ...
The IDLH concentration range used in the past when certifying MINICAMS, 0.20 to 1.50, and the concentration range required in the future, 0.50 to 2.00, are represented by range bars on the diamonds; (3) The CDC's 1988 TWA AEL and the CDC's 2003 15-minute STEL for VX (numerically equivalent to the 1988 TWA AEL)
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From page 49... ...
DAAMS samples are also analyzed to confirm or and non-stockpile sites include a precolumn and an analytical deny TWA alarms sounded by NRT monitoring systems. column in series.
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From page 50... ...
gas chromatographs and the larger mass of agent that can be collected using DAAMS methods, which results in a greater Other automated NRT monitors that have been used or signal-to-noise ratio. For example, as noted previously, tested at various storage and disposal sites include a monitor during one 22-month period at the NECD FPF, about 1.5 per- based on the Dynatherm ACEM 900 thermal desorption unit cent of the VX readings reported by MINICAMS, corre- connected to an Agilent 6890 GC and a newer, improved sponding to 80 different events, were greater than or equal to NRT monitor based on the Dynatherm IACEM 980 unit and the alarm level set point (0.70 TWA)
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From page 51... ...
. Moreover, it would not solve the main problem with One other issue that must be considered is the protection MINICAMS at the NECD former production facility-factor of 50 that is assigned for negative-pressure respirators, namely, the false positives caused by the presence of phossuch as the M40 mask.
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From page 52... ...
Concentration ranges for DAAMS methods used to monitor at 1988/1997 AELs for VX are shown in Recommendation 4-1: To reduce false positives when Figure 4-2. The CDC's 2003 WPL value for VX is less than monitoring at critical locations susceptible to chemical inter- the CDC's 1988 GPL for VX, but it falls within the concenferences, the Army should explore ways to improve the gas- tration range over which current DAAMS methods must be chromatographic resolution of the MINICAMS.
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From page 53... ...
This work addressed both FPDVX is expected to result in improved selectivity and fewer based screening systems used for routine DAAMS monitorfalse positives. ing and FPD/MSD-based DAAMS, which are typically used In anticipation of the implementation of the CDC's 2003/ to confirm the detection of agent by other DAAMS or by 2004 AELs, the Army has conducted tests of modified NRT monitors.
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From page 54... ...
false positives that has sometimes plagued MINICAMS 21It should be possible to configure the A/DAM system with a PFPD or at the NECD former production facility, which was thought an XSD, but -- to the best of the committee's knowledge -- these configura tions have not been tested. It should also be possible to configure the A/DAM system with an MSD or with an FPD and an MSD, but these con 19William Brankowitz, PMNSCM, Information provided to the com- figurations are not practical for routine NRT monitoring, primarily because mittee, May 6, 2004.
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From page 55... ...
, differential IMS, and dual-cell IMS; quate for detecting VX and HD at the CDC's 2003/2004 · Cylindrical ion-trap mass spectrometry and IMS/timeAELs, they are not expected to be sufficiently selective to of-flight mass spectrometry; pass published P&A requirements, to pass initial and con- · Surface-enhanced Raman microwave spectroscopy, tinuing baseline certification requirements, and to achieve terahertz and millimeter-wave microwave spectroscopy, the required statistical response rate at reportable limits when and Fourier-transform microwave spectroscopy; they are used to monitor at the 2003/2004 WPLs for these · Cavitands and liquid crystals; agents.22 Thus, although sensitive enough to detect the WPLs · Ceramic-metallic (cermet) solid state sensors, surfaceand pass P&A requirements for the agents alone, the acoustic-wave (SAW)
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From page 56... ...
this alarm level, NRT systems in use by the Army typically The paper study should be done by technical personnel with have at least a 99 percent probability of reporting a detected extensive hands-on experience in air monitoring at the 1988 concentration greater than or equal to 0.20 STEL and of AELs, who -- along with personnel involved in the manufac- sounding an alarm any time the true concentration of agent ture of miniature mass spectrometers -- should also conduct in the area being monitored equals or exceeds 1.00 STEL. the effort to develop or modify mass spectrometer systems for NRT monitoring.
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From page 57... ...
achieved, the alarm level must be set to a value that The CDC's 2003 Federal Register announcement regard- results in a statistical response rate of 95 percent, and ing AELs for G and V agents states as follows: 24 a first-challenge pass rate of 75 percent must be main tained. In implementing the WPLs, STELs, and GPLs, specific In other words, for a given NRT monitor, according to the reduction factors for statistical assurance of action at the exposure limits are not needed because of safety factors CDC, the alarm level may be set at 1.00 AEL if at least 95 already built into the derivation of the exposure limit.
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From page 58... ...
the NRT monitors performed poorly. If the alarm level had Because of variations in the distribution of agent concen- been set to 0.70 TWA, however, the 1.00-TWA challenges tration readings, if the alarm levels are set to 1.00 AEL, the would have resulted in alarms 100 percent of the time for percentage of 1.00-AEL challenges that result in an alarm both agents for both instruments, which would correctly will vary widely from instrument to instrument and from day reflect the excellent performance of the MINICAMS during to day.
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From page 59... ...
This seems to be a relatively minor reduction in the by MINICAMS are typically biased and are not normal rate of false positives (false alarms) , achieved by increasing over an operating period of several days, the percentthe probability of a false negative for a true agent concentra- age of 1.00-AEL challenges that result in an alarm will tion of 1.00 TWA from about 20 percent to about 50 percent vary widely from instrument to instrument, from day (for an unbiased, normal distribution)
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From page 60... ...
The only per the CDC's 1988 TWA values and at the IDLH levels ceived benefit of raising the alarm level to 1.00 AEL is a for more than 20 years -- with alarm levels set at 0.70 reduction in false positives, but this benefit is gained at the AEL or less. The alarm levels used in the past ensured expense of a higher probability of false negatives, which is at least an 80 percent probability of sounding an alarm unacceptable.
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From page 61... ...
· All DAAMS results are essentially historical; the event · NRT monitoring systems provide an immediate warn- or situation that caused the detection of agent by ing to workers to allow them to take proper actions to DAAMS has likely been detected by other means and protect themselves and to get the situation under corrected by the time the DAAMS sample is analyzed. control, and the setting of an alarm level is the key
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