Severe thunderstorms and the hail that accompany them present a peril that risk managers should not ignore, according to loss control experts.

Munich Reinsurance Co. released an analysis of catastrophe-related insured losses during the first half of 2012 showing that severe thunderstorms caused an estimated $8.8 billion of the total of $9.3 billion in catastrophe-related insured losses in the United States during the first six months of the year.

Although Munich Re's analysis included tornadoes in the severe thunderstorm category, the report also noted that a single hail event in the St. Louis area this spring caused about $1 billion in insured damage.

Fortunately, with the right materials and approaches, risk managers and others responsible for loss control can mitigate the damage these perils can wreak.

“Clearly, risk managers tend to focus on the biggest, baddest events, and sometimes they neglect the potential for death by a thousand cuts from these thunderstorms that pop up each year,” said Louis Gritzo, vp of research for Factory Mutual Insurance Co., which does business as FM Global, in Norwood, Mass. He said that situation is particularly true in summer, when conditions are ripe for thunderstorms to occur. “Summer is the perfect time for risk managers to look for anything that can be damaged by wind or hail,” he said.

A structure's roof is the first line of defense, he said.

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Tim Reinhold, senior vp of research and chief engineer for the Tampa, Fla.-based Insurance Institute for Business & Home Safety, said that different types of roofs present different pluses and minuses. He cited built-up roofs, metal roofs and membrane-type roofs as examples.

A built-up roof typically has gravel atop it, which can blow off in high winds, he said. Such roofs, however, are more resilient than other types to hail.

Metal roofs are very strong, but long metal roofs can be weakened by thermal expansion and construction, he said.

Membrane roofs feature a layer of polymer-type material, like a bigger, stronger tarp that goes over the roof, Mr. Reinhold said. The advantage of such coverings is that they are less expensive than other types of roofs, but the disadvantage is that “you really have to get the fastening right,” he said. If there aren't enough fasteners in the middle, the roofs can balloon.

He said that in a typical business, the risk manager will hire a professional to conduct an assessment of the roof, looking for such hazards as water leaks. The roofer will check the flashing and the roof, and evaluate the roof and look at its condition.

It's key to use the right products and to install them correctly, FM Global's Mr. Gritzo said. Products have to be certified to the level of hazard that is right for the area, he said. FM Approvals, a member of the FM Global Group, certifies products.

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He said risk managers need to look for vulnerable areas such as skylights and asphalt shingles. In addition, they should make sure that any equipment on the roof is securely fastened. Other high-value items that need to be protected should be fastened, moved indoors or covered.

Glass should be treated with film that works like safety glass in a car, Mr. Gritzo said. The glass itself may be damaged, but the film will prevent water from entering the structure, he said.

Another issue to consider is power, Mr. Gritzo said.

“Having a backup power system is always a great idea,” he said. “I would consider that as part of a risk manager's emergency response plan that will serve them for all of their perils,” whether windstorm, snow storm, ice storm or a mild hurricane.