Thieves have been stealing copper for years as prices have risen, mostly an expensive nuisance. Now they are targeting aluminum products, with experts saying safety is at risk as everything from light poles to highway guard rails are disappearing.

"Aluminum prices are at an 18-year high," said Chuck Carr, vice president of member services for the Institute for Scrap Recycling Industries.

Thieves in April made off with $4,000 worth of aluminum bleachers — enough seating for 100 people — from P.C. Campana Park in Lorain, Ohio.

Highway guardrails and light rails have been stolen for years on the East Coast but "now it's everywhere. It's worldwide," said Matt Haslett, spokesman for Metro Metals Northwest of Portland, Ore.

Officers are even staging metals theft stings. In Westminster, a Denver suburb, officers took aluminum park benches to a salvage company, where two employees allegedly paid $33.65 for 58 pounds of the metal. The Benson and Benson Metals Co., pleaded guilty to theft by receiving and will pay $500 to a food bank.

Strong demand from Asia, especially China, is driving the metals market, said Robin Adams of CRU Strategies in Seattle. He contends the mining industry was caught by surprise by demand and can't keep up with supplies of basic metals.

The trend is likely to continue for a couple of years, Adams said. Other metals would be stolen, too, but it isn't practical.

"Aluminum and copper are the ones that stand out. They are on highways," Adams said.

In the past year, copper water spouts have been taken off churches. Coils of communication wires. Power cables for trolleys. Raw copper from the Navy at Pearl Harbor. Authorities attribute at least five deaths to thieves being electrocuted. Railroads have sent out warnings about thefts of spikes, communication equipment and track.

In Idaho, some of the thefts have been linked to methamphetamine users. In San Joaquin County, Calif., nearly $300,000 in metals thefts have been reported this year alone.

"We are going to make periodic checks of our junk and recycling dealers to make sure they are keeping records of who they buy the copper or aluminum from," sheriff's spokesman Les Garcia said.

Carr's institute and its members are taking their own steps to control the thefts. He said many dealers work with police to set up stings.

"A lot of our people are having to hire security guards because people are breaking in," he said.

Haslett's company, meanwhile, is videotaping all its purchases.

"We stall sellers of stolen material and call police. If it is moderately suspicious we will ask the seller to provide some documentation," he said.