Explosive Testing of Window Systems – the Underlying Double-Standard

Test Methods

Explosive testing is typically performed in either shock tubes or in large-scale, open-air arenas.  Shock tube testing is generally less expensive but is not as realistic as open-air tests.

Shock Tube Testing. During shock tube testing, the test specimen is mounted at the end of a structural tube.  A pressure pulse, generated at the opposite end of the tube from the test specimen, travels down the tube and impacts the test specimen.  Pros and cons of shock tube testing include:

Pros:

• Less expensive than large-scale arena testing when testing only a few samples
• Readily reproducible loads
• Can be conducted quickly

Cons:

• Generally limited to one specimen per test
• Generally limited to relatively small test specimens
• Difficult or impossible to achieve realistic open-air blast waveforms (typically the positive phase impulse may be too high and negative phase effects cannot be consistently replicated)
• Difficult to obtain high-quality video footage of the response

In general, shock tube testing can be a useful tool for conducting expedient, inexpensive snapshots of the hazard mitigation potential for small specimens.  However, a full-scale specimen will most likely have to undergo open-air testing to receive true validation within the government and commercial markets.

Large-Scale Arena Testing

Large-scale arena testing is conducted on an outdoor test bed using actual high-energy explosives and full-scale test specimens.  The pros and cons of large-scale arena testing include:

Pros:

• Large size (often full-scale) specimens may be evaluated.
• Multiple specimens may be evaluated simultaneously, reducing overall cost per specimen.
• Replicates actual explosive environments, resulting in realistic blast loading that includes both positive and negative phase.
• High quality video footage of the response is typically obtained, providing good scientific data, as well as dramatic marketing/demonstration video.

Cons:

• More expensive than shock tube testing when testing only one or a few samples.
• Adjustments to the test structure and/or charge size may be required to avoid reduced impulse due to clearing effects when using smaller test structures.
• May require longer lead times in test planning.
• Some variability in results due to real-world environment.

In general, large-scale arena testing allows documentation of a real-world response of multiple, full-scale test samples in an actual, high-energy explosive environment and generally provides more validity in both the government and commercial markets than shock tube testing.

Both the ASTM and GSA test standards allow the use of either shock tube or large-scale arena testing.