The 'official' Lightning operating altitude limit was 56,000ft and the Partial Pressure Assembly was cleared to that altitude. The basic assembly comprised:
Helmet and oro-nasal mask
Partial Pressure Jerkin
Internal anti-G trousers
Obviously, a Breathing Gas Regulator with the necessary Positive Pressure Breathing delivery performance (70mmHg) was also required.
The Taylor Helmet was never issued to all. One of its functions was to reduce neck distension during positive pressure breathing, which can be quite visually dramatic. However, the Helmet had a 'soft' construction at the rear, so precious little head protection from a head-box impact during ejection. Eventually, it gently 'faded away' since a correctly fitted and adjusted, standard helmet and P/Q oro-nasal mask was adequate for the rapid decompression pressure breathing requirement.
The efficacy of the Partial Pressure Assembly above 56K ft falls away quite quickly, plus the issue of ebullism (body fluids 'boiling') becomes a major factor. Hence, a Full Pressure Assembly is sensibly required for acceptable decompression protection once routine operations at altitudes greater than 60K ft are intended.
The confidence most Lightning pilots placed in the aircraft pressurisation system as they punched up to altitudes above 60K ft - without even a Partial Pressure Assembly - was well founded as I cannot recall any failures. However, had there been a rapid decompression at those altitudes, unconsciousness could have occurred in seconds and the effect of 70mmHg of positive pressure breathing on lungs lacking any counter-pressure would not have been beneficial!
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Last edited by lightningmate; 9th Apr 2014 at 13:05.