Research investigated
the effect of a previously identified key containment boom characteristic on
boom performance. Ohmsett testing examined the relationship between boom
performance and buoyancy to weight ratio, as measured by first loss and
gross loss tow speeds. These carefully controlled tests were compared to
previous data on boom performance collected both at Ohmsett and elsewhere in
controlled tank tests and during at-sea trials. The spill response community
has expressed concern with low buoyancy to weight ratios allowed under
existing U. S. Coast Guard response regulations as well as the minimum
ratios specified in the ASTM boom selection standard. The standards were
approved with a note the “buoyancy to weight ratios greater than those
listed in the table may result in improved boom performance under certain
conditions, however, further research is required before minimum values
greater than those shown in the table can be established.”
In testing, A fence-type
boom was prepared with the ability to vary its floatation and eight
elements. However, only a minor variation in buoyancy was achieved with the
result that little variation in boom performance was observed.
With the curtain-type
boom, buoyancies ranged from 3.8 to 10.4, which covers the range of interest
for booms to be used in near-shore and protected waters. There was a
significant decline in performance, as measured by first and gross loss tow
speeds, with less buoyant booms. All booms had essentially the same
performance when operated in calm conditions, first loss speeds of
approximately 0.85 knots and gross loss speeds of 1.0 to 1.1 knots were
observed. When operated in regular and harbor chop waves, the first loss tow
speed was in the order of 0.5 knots and the gross loss speed was in the
order of 0.6 knots for the less buoyant boom, while the values for the more
buoyant booms declined only slightly.
The results of these
tests could affect not only U. S. Coast Guard regulations, but MMS reviews
of spill response plans. Results may also be used by the ATSM in developing
revised standards for containment booms. Requiring improved, minimum
standards in the areas of buoyancy to weight ratio could improve the
effectiveness of mechanical spill clean up operations.
|