By 1979, the Air Force was finding it more and more difficult to site hardened aircraft shelters [HAS] in compliance with then existing existing explosives safety criteria. Those problems were primarily related to real estate constraints and the AF's operational need to place HAS closer to runways and taxiways. Though a number of HAS-related tests and analyses had been conducted between 1969 and 1977, for a number of reasons these tests and analyses only provided limited data capable of supporting further reductions of HAS QD criteria.
Siting criteria were primarily based on the Concrete Sky Phase IXB Test that was conducted in 1971. That test used a single detonation of 4,632 pounds Net Explsive Weight and a fueled aircraft in an open-ended SEA-type shelter constructed of un-reinforced concrete. By contrast, the HAS constructed in the 1970s were made of reinforced concrete and had reinforced bulkheads and front closure systems. It was felt that these structures were capable of offering more protection, both as explosion sources and as targets, than criteria acknowledged. By closely working with the DDESB, the AF was able to obtain some relief from the then current HAS siting criteria.
However, in order to obtain further DDESB-approved QD reductions, additional testing was required. In 1979, the AF initiated the Aircraft Shelter Explosive Test (ASET) Program to develop better QD for HAS. The overall goals of the ASET Program were to: 1. Assess the capability of HAS to protect internal assets (aircraft, munitions, and personnel) from external weapons effects (airblast and ground shock); 2. Assess the capability of HAS to prevent or suppress propagation; 3. Assess collateral damage effects to and vulnerability of nearby runways and taxiways.
The ASET test program was named DISTANT RUNNER and was separated into two phases. The first phase was to investigate the response of two full-scale 3rd Generation HAS to an external pressure loading, and the second phase was to investigate an internal pressure loading. A total of five tests were conducted. Some sources state that the Distant Runner test consisted of a single detonation of 2,250 tons [2,041 metric tons] of ANFO, but this is evidently in error.
Event 1 exposed a HAS to an internal detonation of 42 pounds NEW (four Sidewinder (AIM-9) warheads). This weapon arrangement was selected to simulate a weapons load for an aircraft loaded with air-to-air weapons. The primary objective of this test was to demonstrate the ability of a 3rd Generation HAS to completely suppress all effects resulting from an internal detonation involving four AIM-9 missiles.
Event 2 exposed both HAS to an external loading of 15 psi produced by the detonation of 240,000 pounds of Ammonium Nitrate/Fuel Oil (ANFO). One of the HAS was oriented side-on to the blast, while the second HAS was oriented rear-on to the blast. Obsolete aircraft were located inside the HAS. The primary objectives of this test were to demonstrate that a 3rd Generation HAS could withstand an external pressure loading of 15 psi in rear-on and side-on orientations to the detonation source, and to demonstrate that a 3rd Generation HAS could prevent internal pressure buildup in these orientations.
Event 3 exposed one of the 3rd Generation HAS to an external loading of 15 psi and the other to an external loading of 7.8 psi produced by the detonation of 240,000 pounds of ANFO. The HAS exposed to 15 psi was oriented head-on to the detonation source, while the other HAS was oriented at an oblique angle (26 degrees off normal) to the detonation source. Obsolete aircraft were located inside the HAS. The primary objectives of this test were to demonstrate that a 3rd Generation HAS could withstand external pressure loading of 15 psi in a front-on orientation and 7.8 psi in an oblique orientation to the detonation source and to demonstrate that a 3rd Generation HAS could prevent internal pressure buildup in these orientations.
Event 4 exposed a HAS to an internal pressure loading from the detonation of 2,292 pounds NEW (12-MK 82 bombs) inside the HAS. The primary objectives of this test were to demonstrate the blast attenuation characteristics of a 3rd Generation HAS, exposed to an internal detonation involving 2,292 pounds NEW, to evaluate debris distances, and to determine the structure's failure mode.
Event 5 exposed a HAS to an internal pressure loading from the detonation of 9,168 pounds NEW (48 MK 82 bombs) inside the HAS. The primary objectives of this test were to demonstrate the blast attenuation characteristics of a 3rd Generation HAS, exposed to an internal detonation involving 9,168 pounds NEW, to evaluate debris distances, and to determine the structure's failure mode.
A common secondary objective for Events 2 through 5 was to assess/evaluate the damage (from ground motion effects and fragmentation) to the runway /taxiway as a result of each event.
DISTANT RUNNER results supported the reduction of QD for: 1. Side or rear of an ECM (275,000 pounds NEW TNT) to a 3rd Generation HAS from K30 to K5; 2. Open storage (100,000 pounds NEW TNT) to a 3rd Generation HAS from K30 to K8; 3. ECM (275,000 pounds NEW TNT) to a taxiway/runway from K18 to K4; 4. Open storage (100,000 pounds NEW TNT) to a taxiway/runway from K18 to K4.
DISTANT RUNNER results were unable to support a reduction of QD for HAS to occupied (inhabited) structures, but instead demonstrated a need for increased separation distances. Consequently, increased QD was required as follows: 1. Distance (d) = 50 W1/3 from the front of a HAS; 2. D = 62 W1/3 from the sides of a HAS; 3. D = 40 W1/3 from the rear of a HAS.
At the 283rd Meeting of the DDESB, which met on 19 January 1982, the AF presented their rationale as to why the separation distances between HAS and ECM, approved previously by the DDESB for 3rd Generation HAS, should apply to all HAS, except the door of a 1st generation HAS. DDESB approval of the proposed AF changes can be found in 1 February 1982 DDESB-IK memorandum.
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