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Technical Requirement - The overall objective was to emplace a blast shelter supplied by B C Barton and Son Ltd and subject it to a representative bombardment hazard and to demonstrate its protective capability. This requirement was considered and executed in the following specific tasks:
- Emplace the blast shelter.
- Subject it to a representative salvo of five 155mm (~6") shells (M107 RDX TNT). (See TRIAL SCHEME)
- Examine and photograph the effect of each round on the emplacement.
- Measure, inside the shelter, the peak sound and pressure from each round.
- Detonate additional rounds close to the shelter to explore the ultimate strength of design.
Results
Structural Effects
 The damage of each successive round is shown with distortion varying between 30mm deflection of the 1.5mm plates (Round 1) and 0.5m deflection on the end plates (Round 4) with some separation of the bolted joints and intrusion of the clay soil.
 Also illustrated is the Armour plate hatch cover showing the effect of fragmentation from the air burst. It may be noted that both the 8mm and 10mm mild steel plates were penetrated but the 4mm Armour plate hatch cover remained undamaged, but showed scoring from the impact of fragments.
Blast Effects (over pressure)
 The foil gauges were examined after each round and found to be not ruptured and therefore the overpressure within the shelter remained below 14 kPa (1.8 psi). The overpressure exerted by the ground bursts was 134 kPa (19.5 psi).
Peak Sound Level
The peak sound level from each round was recorded as shown in the table below.
| Firing No.* |
Sound Level/dB |
1 |
not recorded |
2 |
140.0 |
3 |
147.2 |
4 |
146.0 |
5 |
150.0 |
*Refer to TRIAL SCHEME for location of shells
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The results show that no damage to the human ear or chest cavity would occur. The lowest limits for permanent damage to these being:-
Ear:- 15 kPa (2.2 psi); Chest Cavity:- 140-220 kPa (20.3-31.9 psi).
Conclusions
a. Structure
- The shelter is compact and easy to emplace.
- It has the necessary strength and resilience to be used for protection of personnel and equipment against the hazards of the severity covered by this report at distances of 5 meters and above.
- Its inherent capability of progressive collapse against hazards of increasing severity is a distinct advantage over more rigid structures which may fail catastrophically (i.e., total collapse of one or more walls).
- This resilience also prevents internal structure fragmentation (which may be produced by failure of reinforced concrete) which would be dangerous to personnel.
- The condition of the soil was heavy and wet clay provided a good coupling between the explosion and shelter.
- The entrance hatch provides adequate protection from air bursts of the severity covered by this report.
b. Human Factors:
AWRE analysis, based on the evidence of the experiment, leads to conclusion that human personnel within the shelter would survive all instrumented rounds. The hazard caused by detonation was well below that necessary to cause damage to most sensitive parts of human structure, i.e., ears and chest cavity.
Recommendations
- The shelter, being a light structure, is suitable for a cost-effective emplacement.
- The strengthening of the ends by webs, ribbing and more bolts would improve the shelters capability to withstand explosive shock at distances of less than 5m.
- Where it is assessed that the hazard is much greater than covered by this report the shelter would be an excellent liner for a more rigid structure, e.g., reinforced concrete where it would provide protection against the fragmentation hazard.
- The addition of a 'soft' lining would improve the sound attenuation and hence personnel comfort but is by no means necessary for survival.
Acknowledgements
- Thanks are extended to all those who provided the necessary advice and assistance for a successful trial In particular, thanks go to the dedicated support, in appalling weather conditions, of the Royal Engineers, the Department of Operational Analysis photographers and to Mr. B. S. Freeman.
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