Neil Ham MSc – Emergency egress subject matter expert – explores the condition of spatial disorientation and concludes how vital lessons learned from the air domain can help to save the lives of land personnel traveling in armoured vehicles.
By Neil A Ham MSc, Technical Lead & Co Director AeroGlow Int Ltd.
“Spatial Disorientation” - is the human inability to maintain the body’s orientation and/or posture in relation to the surrounding environment (physical space) at rest and during motion.
Both the US and UK Military are now recognising the operational risks of operating near wadis, canals, and irrigation ditches, and are acting accordingly. Unfortunately the water found in these scenarios is likely to be extremely turbid which has compounded the associated safety requirements for escape lighting. The cabin spaces within many armoured vehicles are comparable to that of a support helicopter; such that there is space for crew to become easily dis orientated in an event. The risks associated with IED attacks and basic night operations are also at the forefront of safety concerns by armoured vehicle operators. Land vehicles are notoriously prone to roll-over, and are also suffering the threat of IED attacks in Theatre. In these situations spatial disorientation is also becoming recognised as a key risk; this risk obviously being compounded by the presence of thick smoke and/or darkness.
Although dunker training is yet to propagate into armoured vehicle programs, UK and US soldiers entering Theatre do receive live roll-over training. Large roll-over simulation devices allow troops to progressively experience the disorientation, discomfort, and chaos associated with actual vehicle roll-overs. However, appreciation of these events does not wholly mitigate the risks associated with spatial disorientation. In a real scenario, should smoke be present in the cabin, as with water ingress, crew will need to orientate almost instantly as they will have only seconds to escape before panic leads to asphyxiation. It is these vital few seconds that hold the key to taking effective mitigation measures. Taking lessons from the air domain the UK MOD have now fitted water, smoke, blast and roll-over activated egress lighting to all UK operated roll-over trainers known as the RODETs (Roll Over Drills Egress Trainers). Egress lighting has also been procured by the UK MOD for a large majority of Theatre standard vehicles - some 2000+ systems. US Special Forces also operate a similar number of systems.
Mandatory requirements for Land based Armoured Fighting Vehicles to employ emergency egress lighting has been published [DefStan 00-25 Part 14 -10.5.5.4]. Egress lighting is intended to maximise the survivability of the crew by automatically illuminating all vehicle escape hatches, handles and vital escape equipment (such as spare air supplies). A proven configuration derived from the air domain is to have an inverted U around egress points to effect rapid spatial orientation, red lights to indicate safety equipment (for example battle locks) and green lights for door opening levers. Lighting must be effective through thick smoke, and turbid water. A major breakthrough in the military land domain in recent years has been acceptance of some of the lessons learned from the air domain, particularly helicopters with flight over water clearances.
One of the first historical tasks undertook by AeroGlow SMEs (in the air domain) was to assess the use of photo-luminescent tape (glow in the dark tape) as a potential egress lighting aid for helicopters. Use of the tape was hoped (by MOD) to be be a quick and inexpensive solution for the air platform in question. This assessment included testing using live subjects in turbid water trials to advance emergency egress knowledge.
Results showed that photo-luminescent tape can rapidly loose its charge in cold temperature. Dropping a sample of fully charged tape into icy cold water is the most effective way to assess this phenomenon. Also, although the tape can be seen reasonably effectively in clear air at night when the human eyes are dark adapted, it cannot be seen effectively even in clear warm water by the naked eye. The human eye requires an air gap to focus on its intended object. In water without a diver’s mask the light given from glow tape was found to be not concentrated enough to penetrate and register on the retina. An observation from this assessment noted that fully charged PLT could be seen clearly on the bottom of the pool by onlookers (on the poolside), but could not be seen by test subjects underwater - even when placed only inches away from the subjects eyes.
The photographs below are more recent examples taken from internal smoke testing of LED point source lights in comparison to alternative lighting technologies. During this test a constant level of smoke was maintained. This was produced using a glycerine/water mix. The distance from the source was marked at increasing test points. Photographs of the systems were taken from increasing distance using equal exposure and shutter settings. The technologies were as follows: a) Glint/reflective tape (with a torch as the source); b) Photo-luminescent (glow) tape; c) Electro-luminescent charged strip; d) Point source LED based system at optimum frequency.
The above extract illustrates how appropriately designed point source LEDs can penetrate light long distances even in turbid mediums. Glint tape and photo-luminescent (glow) tape simply are not bright enough to have a positive effect. Electro-luminescent strips do offer some benefit and interestingly are often used in helicopters; however, the lack of a bright point source impacts its ability to be effective over longer distances; the reason that these lights are still used in helicopters is probably due to fairly old standards such as MIL-PRF-85676A, which are arguably in need of review. Obviously LED lights that are too bright should be avoided as to avoid dazzling personnel in favourable conditions. LEDs are most effective in the region of 7000 cd/m2, but also need to be mounted with an effective arc of visibility within an appropriate frequency.
The key point to note here is that emergency egress lighting is only vital in two scenarios - if there is either smoke, or water presenting a hazard to crew. In these situations glow tape will not provide realistic risk mitigation.