Interruptible Gas

Firm services, also called uninterruptible services, are services, such as electricity and natural gas supplies, that are intended to be available at all times during a period covered by an agreement. Also, the service is not subject to a prior claim from another customer and receives the same priority as any other firm service. Conditional firm service is similar to firm service in that it is reserved and has priority over interruptible service. However, it can have restrictions, such as times when it would be curtailed before firm service but after interruptible service. The cost per unit with this service is called a firm rate or uninterruptible rate. The opposite of firm service is non-firm service, also called interruptible service or as available service. The cost per unit for this service is called a non-firm rate or interruptible rate. The interruptible load is the portion of a utility's load that comes from customers with interruptible service.
See more at Wikipedia.org...

A gas supply, usually to industrial plants and large commercial firms, that can be curtailed or interrupted during emergencies or supply shortages in order to maintain service to domestic customers.

Gas sold to customers with a provision that permits curtailment or cessation of service at the discretion of the distributing company under certain circumstances, as specified in the service contract.

Gas made available under agreements permitting the termination or interruption of delivery by the suppliers, usually for a limited number of days in a specific period. The opposite is "firm gas".