A flood of lawsuits is damaging companies that make respirator masks for emergency workers during a terrorist attack or airborne epidemic, says a Pennsylvania congressman who is behind a bill to grant the manufacturers immunity from injury suits if the federal government has certified a mask to be safe, reports theMinneapolis Star Tribune.

According to the report, 3M has faced more than 408,000 injury claims over disposable dust masks it sold for more than 25 years.

Last year, 3M said it had paid nearly $300 million to resolve about 300,000 respirator claims. As of March 31, it had resolved another 50,000 claims, according to the report.

The immunity bill would prohibit suits that blame respirators for any toxic exposure — from silica dust and coal dust to deadly anthrax and the potentially lethal avian flu and SARS viruses.

Its chief supporters are six other respirator companies that formed the Coalition for Breathing Safety. A coalition spokesman told the Star Tribune member companies don't want to be identified because "they don't want to become targets" of more suits.

Between 2000 and 2004, five of those companies were named in 326,215 injury claims, most of which are pending, the coalition told the paper. Many of the claims were filed by silica-dust victims who each sued dozens of companies but "show no real signs of illness," according to the coalition.

The coalition says none of the manufacturers is facing bankruptcy because most claimants seek small settlements.

A Minnesota lawyer who has sued 3M over its respirators called the bill "ridiculous" because it defines a mask as safe if approved by NIOSH or, before 1972, by the U.S. Bureau of Mines. Before NIOSH adopted new, more rigorous tests for disposable respirators in 1995, he said testing standards were not accurate in determining the effectiveness of disposable masks to filter out the smallest of particles.

Lawyers for 3M have vigorously contested those allegations, saying the company's 8710 model was highly effective when used properly, according to the newspaper account.

Under the bill, a plaintiff could sue only if he could prove that a manufacturer knew its product was defective and did not meet NIOSH standards.