Blast-resistant building ratings: Is high response acceptable?

In the blast-resistant building industry, we toss around the term “response level” all the time and assume everyone knows what it means. And maybe everyone does, but the difference between a low response building and a high response building can mean the difference between life and death, so it’s worth a closer look, even if you already know the basics.

‘Response level’ equals ‘damage level’

Response levels are ratings established by the American Society of Civil Engineers (ASCE) to predict the extent of repair resources that would need to be devoted to a building after an explosion. Their descriptions include:

  • Low response — Localized building/ component damage; building can be used, however, repairs are required to restore the integrity of structural envelope; and the total cost of repairs is moderate.
  • Medium response — Widespread building/component damage; building cannot be used until repaired; and total cost of repairs is significant.
  • High response — Building/component has lost structural integrity; building may collapse due to the environmental conditions; and total cost of repairs approaches replacement cost of building.

Substitute the term “damage level” for “response level,” and it gives you an instant picture of what these ratings mean. Given the options of low damage, medium damage and high damage, you obviously don’t want to be working in a high damage facility during a blast event. Anything worse than medium response is virtually synonymous with injuries and fatalities. And if you plan on using the building to house critical control systems in a petrochemical facility, casualties are only one of many problems you’ll face in a high response situation.

What to look for

There are several blast-resistant building designs on the market. When we were asked by one of the industry’s key oil refiners to come up with a new one, our first step was to study what was already out there. It came as a surprise few of the existing designs had received low response ratings from ASCE. We hired Ali Sari, Ph.D., PE, one of the few experts in the world with firsthand blast response experience, and the resulting RedGuard designs were awarded low to medium response ratings, depending on blast pressures.

How did we achieve this? The most significant improvement is the placement of steel studs 11 to 12 inches apart rather than several feet apart. This denser stud framework is like a boxer’s rib cage, which springs back after taking a punch. Place too much flat wall surface between studs, and response ratings rise quickly.

Are regulations in place?

There is no regulatory board for blast resistant building design because the technology is still new. This will probably change, but the closest industry criteria currently in place are the recommended practices provided by API. These design considerations are aimed at meeting specific psi and duration requirements for specific zone placements, but that only covers two out of three vital criteria. There is still room for confusion when building manufacturers meet the required pressures and durations for specific zones but incorporate a high response level in their design.

Even with these important guidelines in place, the final proof is in the testing. We detonated 1,250 pounds of high explosive ammonium nitrate/fuel oil charge at a standoff distance of 110 feet from our building, which created a blast strength far in excess of the ratings required to meet ASCE low to medium response standards. The building suffered no structural damage and neither did the furnishings, office equipment or test dummy we placed inside.

This outlines the importance of taking a closer look at both response level ratings and test results before you buy a blast-resistant building. At RedGuard, we manufacture our buildings as if we’ll be using them ourselves. If your goal is to protect personnel and resources, you should ask yourself, “Is high response good enough?”