State hazardous waste officials have given Hercules Aerospace emergency permission to store explosives used in the manufacture of solid rocket motors because of the shutdown of a treatment facility for safety reasons, officials say.

The action extends the existing temporary permit of the Magna company, allowing it to store waste ammonium perchlorate and HMX for 90 days.The volatile materials are used in the manufacture of solid fuel motors for military and civilian rockets, Hercules spokesman Ted Olsen said Friday.

Ammonium perchlorate was the propellant oxidizer made by Pacific Engineering and Production Company at a Henderson, Nev., plant destroyed by an explosion May 4. The company, one of only two U.S. producers of the crucial oxidizing agent, has begun construction of a new plant near Cedar City.

"Hercules cannot use its own open burning-detonation grounds for treatment of this particular waste because of the difficulty in treating the waste and the potential endangerment to human health and the environment by unexpected detonation," said William Sinclair, permits section manager in the Utah Bureau of Solid and Hazardous Waste.

Under its existing permit, Hercules can store the materials for less than 90 days.

"Hercules was shipping the waste to an off-site treatment facility until recently when some safety problems temporarily shut down the facility," said Sinclair.

But officials expect investigation of the treatment facility to be completed and "the problem resolved before expiration" of Hercules' 90-day emergency permit, he said.

Hercules manufactures solid-fuel motors for the Trident 2 missile, the MX or peacekeeper intercontinental ballistic missile and the small ICBM, as well as for the non-military Delta 2 and Titan 4 boosters, Olsen said.