1. Results of Analysis by Independent Mass Spectrometry Experts
a. US Army Chemical and Biological Defense Command Analysis
The US Army Chemical and Biological Defense Command responded:
Both MM1 tapes indicate valid detections of the riot control compound known as CS. We assign a high confidence level to this conclusion....
[The] initial response of the first MM1 was an alarm to the chemical warfare compound GB (sarin). From the tape copies provided, we cannot determine whether CS was being monitored for in the wheel high method as the monitor list for this method was not printed out or not provided. In any case, as prescribed by proper Fox NBC Reconnaissance procedures on detection of a chemical warfare compound, the operator programmed the MM1 to take a spectrum of the compound detected. The MM1 then automatically searches its entire library of chemical warfare compounds for the best match of that spectrum. The MM1 then correctly identified the compound as CS, a riot control agent. It must be understood that for a number of complex technical reasons, the MM1 sometimes incorrectly identifies the compound being sampled when it is monitoring in the air monitor mode. For this reason, the spectrum procedure is prescribed to assure correct identification after the initial response.
b. Bruker Analytical Systems, Inc., Analysis
Bruker Analytical Systems, Inc., the manufacturer of the mass spectrometer used in the Fox reconnaissance vehicles, also confirmed that the initial alert for sarin was false and that the full spectrum analyses correctly detected the riot control agent CS. The report states:
I have looked at the tapes you have supplied in your FAX of 28 September 1996, and can state without a doubt that the substance was CS and not Sarin.
Bruker explained that the two main reasons for the initial alert for sarin are: (1) the monitor modes compare detections of only four ions against a limited target list; and (2) the detectors interference parameter is set so that no alarms will be suppressed for extremely dangerous compounds such as sarin.
Regarding the first factor, the Bruker report states:
In either Air or Surface Monitor Modes, the MM-1 has a TARGET COMPOUND LIST that it is looking for. It is simply monitoring the intensities of the 4 ions in the list of compounds selected. IT IS IGNORING ALL OTHER IONS IN THE SPECTRA.
This means that it is rapidly searching for a fingerprint consisting of 4 ions for each compound. While this mode results in high sensitivity and rapid response, it is important to realize that the accepted legal criteria for identification of compounds by mass spectrometry (for example in EPA methods), requires that a COMPLETE SPECTRUM OF ALL IONS PRESENT be provided. This is one reason why ANY alarm must be verified by the FULL SPECTRUM even though the spectrum will not be as fast to alarm.
In short, the Fox can more quickly sound an alarm by comparing only four ions against a limited list of candidate chemical warfare agents. When the Fox collects the full spectrum and compares it against the 60 compounds in its library, it gives the operator a higher level of confidence in the substance reported by the Fox. But the operator still needs to print the list of all the ions present to make an accurate and conclusive assessment.
Regarding the interference parameter, the Bruker report explains:
The interference parameter suppresses false alarms due to LARGE amounts of other substances present. Since in Air Monitor mode, only a certain list of compounds are monitored, if the ions of one of the other compounds monitored are present in large amounts, then the alarm is suppressed. This blocks false alarms resulting from minor peaks present in the mass spectra. In this case, if the difference between the largest ion monitored and the ions of CS ions is greater than 10 ([inverse] Log 1.0) the alarm is suppressed. For Sarin, the difference must be [inverse] Log 8.0 or 100,000,000. This is typically used to suppress false alarms from petroleum oil in the background. The MM-1 has a dynamic range of Log 8. THIS MEANS THAT WITH AN INTERFERENCE OF 8 FOR SARIN, NO FALSE ALARMS WILL BE SUPPRESSED IN THE PRESENCE OF LARGE AMOUNTS OF OTHER COMPOUNDS- IN THIS CASE CS. Since the standard procedure calls for taking a complete spectra and verifying the identification, some false alarms in Air Monitor mode are accepted by the Army to INSURE that there are NO FALSE NEGATIVES where a dangerous agent such as Sarin would not be detected. In the case of CS, and (sic) Interference of 1.0 means that the alarm may be suppressed due to the presence of other ions.
In other words, the US Army uses an interference parameter that is set sufficiently high to ensure that an alarm will sound for very small amounts of extremely dangerous compounds like sarin in the presence of large amounts of other compounds, like CS. Alternatively, for compounds such as CS, the interference parameter may be set low to prevent false alarms in the presence of large amounts of other compounds.
Moreover, regarding this particular combination of compounds, the Bruker report states:
With the interference and reliability parameters used, it is expected that CS in such high concentration, would give an alarm for Sarin and indicate a lower concentration. This is why a full mass spectrum is considered necessary to identify a substance by mass spectrometry in a court of law. Likewise, this is also why the standard procedure the soldiers are taught for operation of the MM-1 REQUIRES a spectrum for verification. There is no firm identification UNLESS the spectrum identifies the agent. As an analogy, alarming in Air Monitor Mode is equivalent to standing on the side of the road with your eyes closed and identifying makes and models of automobiles passing by the sound of the engine. Spectrum Mode would be equivalent to opening your eyes and seeing the license number, color, and make/model of the automobiles in addition to listening to the engine.
c. National Institute of Standards and Technology Analysis
In agreement with the above analyses, the National Institute of Standards and Technology (NIST), stated that the mass spectra from the two Fox reconnaissance vehicles "are clearly diagnostic of CS - there is no evidence of Sarin. The very low threshold settings for Sarin relative to CS provide a credible explanation of why Sarin was reported [and] was a false identification." The threshold settings, here, refer to the interference parameter discussed above.
The Task Force chemical officer contacted the Office of the Special Assistant for Gulf War Illnesses in July 1997 after this narratives initial publication in May and provided a contemporaneous written statement on the exposure incident. The memorandum, written on September 16, 1991, by the 25th Chemical Company platoon leader and the Task Force chemical officer clearly states the sequence of events, precautionary measures taken, and the testing procedures conducted to assess CS presence. Interviews with both the platoon leader and the chemical officer confirm that explosive ordnance disposal personnel identified the powder as CS, that Fox reconnaissance vehicles tested the substance on two separate occasions and all full spectrum analyses confirmed positive CS, and that all exposed individuals experienced only short term health effects consistent with CS and returned to duty by the next day. One Fox reconnaissance vehicle operator reported seeing a short brown can, approximately 8 inches in diameter with a powdery substance inside. The description of the can was consistent with that given by the chemical officer, platoon leader, and government contractor. Discussions with several of the exposed soldiers also verify that the metal cans contained a powdery substance, that the health effects experienced were acute, and that the symptoms they experienced were of short duration. The Camp Monterey commander corroborated the sequence of events and reported that the government contractor had verified, at the time of the incident, that the Fox reconnaissance vehicles were correctly calibrated and that the agent detected was CS. The Camp Monterey commander also said that the unit physicians assistant reported that everyone was fine, and that there was no evidence of nerve agent exposure.
There are some discrepancies regarding the color of the powder. The official statement and recollections by the chemical officer and platoon leader state that the powder was dark in color, but eyewitness accounts assert that the powder was light-colored. One theory presented by the 25th Chemical Company platoon leader is that the powder was gray and appeared darker when it was amassed together in the canister. When it was dispersed, as the exposed soldiers would have seen, the gray powder would appear lighter in color. Regardless of the powders color, however, testing and analysis confirm positive CS presence.
The results of the initial investigation were provided to the government contractors lawyer in 1996. The attorney has made no further inquiries into the matter.
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