Firm service cannot be interrupted during adverse conditions, such as periods of high demand.
There are extreme cases when firm services may be interrupted, such as emergencies and when system reliability is threatened.
Firm and non-firm service is also available for companies that rent or lease pipeline or electrical transmission capacity.
Firm service for natural gas pipelines and electrical transmission lines often include two charges.
Interruptible rates are volumetric, being based only on the volume of gas or electricity delivered.