The largest test blast in the western Utah training range's history could rattle some windows along the Wasatch Front early in November, the Air Force said, but measures are being taken to prevent damage and to reduce what one official called "the startle factor."

The Air Force will blow up 500,000 pounds of high explosives Nov. 8 on the Utah Test and Training Range, testing a newly designed munitions storage igloo. That's twice the size of the previous rec-ord blast, a 250,000-pound detonation 20 years ago.An environmental assessment prepared for the Air Force predicts residents from Ogden to northern Salt Lake City will probably hear the blast and, under certain weather conditions, some windows could break.

Len Barry, public affairs spokesman for Hill, said weather conditions will be monitored and the test delayed, if necessary, until the right conditions exist to prevent property damage.

Other than that, the test will have no significant environmental impact, according to an assessment prepared by the Air Force in May. The range has been subjected to 40 years of bombing and strafing runs, high explosives blasts and other tests, the assessment concluded, and one more won't have much effect.

The blast is designed to test a new, experimental munitions storage facility called the Hayman Igloo, designed by engineers at Hill. Two igloos will be built 100 feet apart. One, packed with 500,000 pounds of explosives, will be blown up.

Test instruments will monitor the effect of the blast on the igloo containing the explosives, called the donor igloo, and the unit next to it to determine their capability to withstand the blast.

According to the Air Force's assessment report, several hundred new munitions igloos are needed at bases and installations around the world. But the current-style igloos, made of steel-reinforced concrete and poured on the site, take two to four weeks to build and cost $300,000 each.

The Hayman igloos are made of precast concrete panels locked together with steel beams. They can be assembled in one day and, unlike the current models, can be taken apart and reassembled on another site.

Engineers estimate the Hayman igloos cost $60,000, which the Air Force said would add up to a significant savings in light of the several hundred that are needed worldwide.

According to the Air Force's environmental assessment, the only non-military facilities that will likely be impacted by the November blast are the Lakeside Railroad Camp and the state's West Desert Pumping Station.

Personnel at both facilities will be alerted to reduce what the assessment terms "the startle factor."