Part III - Historical Survey of the Porton Down Service Volunteer ...

Site of skin Number of
men
Average total dose (µg)
Average time dose
was left on skin
(minutes)
Palm 8 26 360
Back 8 25 510
Forearm 14 15.7 577
Table 10.1. Liquid VX studies with Service volunteers
ChE depressions observed were small, varying from 1.9% to 3.9%. After a brief delay the
penetration of VX through the forearm and the back was "regular and rapid": on average, 8%
of the VX dose penetrated through back skin and 15% through forearm skin in 8 hours.
10.3. Human studies with VX vapour
10.3.1. Inhalation of vapour
Eight volunteers from the Porton medical staff took part in a study involving the inhalation of
VX vapour in 1961 and 1962. It had been demonstrated in previous work that ChE recovers
to normal levels rapidly after an exposure to VX [37]. Therefore, this study involved the
volunteers being exposed to VX vapour several times. In total the study featured 54
exposures. No man was exposed either for the first time or subsequently unless his ChE was
within normal limits.
Only the head and neck were exposed. Vapour was delivered down a tunnel at the end of
which the subjects placed their head and neck. At the end of the exposure, no washing of the
face or any form of decontamination was allowed for 8 hours.
19 exposures involved men with no respiratory protection. Fifteen of the exposures lasted
either 3 minutes or 1.5 minutes, at 0.6 - 3.6 mg.min/m 3 . The remaining 4 exposures lasted for
6 minutes or 7 minutes, at 4.8 - 6.4 mg.min/m 3 . The following effects were noted [36]:
• the maximum ChE depression observed was 70% in RBC ChE but plasma ChE
was very much less depressed than RBC ChE;
• miosis developed 1-3 hours after exposure and usually passed off 36 hours later.
The remaining 35 exposures involved the same men being exposed but with respiratory
protection: a mouthpiece and a clip over the nose. Twenty five of the exposures lasted
between 1.5 minutes and 4 minutes (exposure levels of 0.7 - 20 mg.min/m 3 ). The remainder
were longer (9 - 24 minutes, 7.7 - 25.6 mg.min/m 3 ). In practical terms, men undergoing these
exposures did not breathe in VX vapour, but the following results were recorded [36]:
• no symptoms were observed during the exposure, although nearly all subjects
developed miosis 30 minutes after exposure;
• ChE was depressed, in two of the exposures by more than 50%.
The second result was quite startling: it suggested that VX vapour was absorbed quite rapidly
through the skin of the face and neck, so that even with protection a man would be vulnerable
to VX vapour. In reviewing this result, the BC noted that VX vapour absorbed through the
skin could be as great a danger to a masked man as GB was to an unmasked man [38].
The study generated estimates of the L(Ct)50 dose in man for VX vapour, based on the
doses necessary to depress ChE by certain percentages [36]. These estimates are
summarised in Table 10.2. The estimates are given as a range as there was disagreement
between the US and the UK on the ratio of L(Ct)50 to doses which induced either 50% or
90% ChE depression. The estimates were not accompanied by an indication of the length of
the exposure.
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