In binary weapons, toxic effect comes only when two chemicals in a warhead are mixed.

A binary weapon is one that contains two separate ingredients, each of which is relatively harmless until mixed.

Most binary weapons contain methyl phosphonyl difluoride in one compartment.

Until the accord is fully in effect, the United States said it would continue to produce and deploy its new binary weapons.

American officials have made clear that the Bush Administration intends to proceed with the development of the binary weapons.

The new binary weapons are considered safer to handle.

This led to speculation that the binary weapons might be inferior to those unitary weapons they were replacing.

Military officials say the artillery shell was a binary weapon.

Called binary weapons, they contain two substances that are harmless if kept apart, but combine to form deadly nerve gas on firing.

Exactly how many tons of new binary weapons will be produced in the future depends on arms control measures and on Congress.