The nation's largest supplier of bullet-resistant vests to law enforcement agencies is urging its customers to replace vests containing the fiber Zylon (search), saying they may not be safe.

Second Chance Body Armor (search) said Wednesday it had sent notices to police agencies nationwide. The warning affects about 58,000 Tri-Flex vests and an additional 40,000 Ultima and Ultimax vests with Performance Pacs, the company said in a statement.

New research shows that vests made even partially with Zylon "may fail to perform and result in serious injury or death," it said.

Second Chance, based in Central Lake, is undergoing reorganization in federal bankruptcy court after being targeted in numerous lawsuits claiming its vests made with Zylon are defective.

The company said it would ask the court to devise a procedure for vest owners to make claims arising from the latest warnings.

"While Second Chance has not received any reports of field failures of the products in question, we felt it was our obligation to report these new research findings immediately," said Matt Davis, vice president of sales and marketing.

"The safety and well-being of all the officers who wear our body armor is of primary importance to Second Chance, and we strongly encourage all officers to replace ballistic vests that contain Zylon as quickly as possible."

Second Chance began making vests with Zylon in 1998, saying it was lighter and more comfortable than other fibers used in body armor. The company announced in 2003 it had concerns about the durability of Zylon vests and recalled more than 130,000 of them made entirely with Zylon.

The latest notice pertains to vests containing a mixture of Zylon and other materials. Ultima and Ultimax vests originally contained only Zylon, but the Performance Pacs designed to boost their effectiveness have other fibers.

Lawsuits against Second Chance have been filed in at least 11 states, and federal and state investigations have been started. Seven lawsuits have been filed by state governments.

Zylon is manufactured by Toyobo Co (search),. a Japanese company also targeted in numerous lawsuits. Toyobo has acknowledged that tests show Zylon loses 10 percent to 20 percent of its durability within two years of manufacture. But the company says the fiber works well in body armor that is properly constructed.

Second Chance said the research that prompted its latest safety notice was conducted by a polymer chemist retained by the company's legal counsel.

Tests designed to determine the cause of the vests' degradation detected unexpectedly high levels of acids that "can lead to a sudden and dramatic loss of tensile strength," the company said.

"These test results lead us to believe that even products that contain relatively low percentages of Zylon by weight may fail to perform as expected," Davis said.