Also known as an uninterruptable service, a firm service is a type of service that is intended to be available on a continual basis, unless factors outside of the control of the provider temporarily suspend access to those services. The term is normally associated with the delivery of such utilities as electricity and natural gas to both residential and commercial customers. The idea is that subscribers are free to make use of as much or as little of the firm service as desired, with no apparent shortages experienced by others who also have access to the same service.
One of the characteristics that defines a firm service is the constant availability. Access is possible at any time, with no limitations placed on the usage. For example, a power grid that supplies electricity to customers is constantly active, adjusting the flow of power to manage the demand. Under ideal circumstances, the grid is in operation at all times, ensuring that customers do not have to worry any interruptions that could cause some sort of inconvenience.
The concept of firm service as part of a public utility system is very important. Priority clients that relay on these types of services in order to operate essential facilities will often be extended what is known as a firm rate and may even have access to special backup facilities that supply services in an emergency. One example of a firm client would be a hospital, in which an interruption of power could seriously impact the ability of hospital staff to care for patients, as well as allow patients using breathing apparatus or other medical equipment to remain stable in jeopardy. When the firm service involved is some type of natural gas, steps are often taken to contain the section of pipeline that is temporarily inoperable, repair the issue and restore the service with a minimum of interruption.
Firm service is different from as-available service, in that the latter may experience scheduled interruptions from time to time and is billed on a carefully measured allocation to users. Typically, an interruption in a firm service is not something that is planned in advance, and will be the result of some sort of mechanical failure, a natural disaster, or any event that is beyond the control of the supplier. In many cases, emergency backup strategies are activated immediately to minimize the duration of the interruption by rerouting pipelines or grid usage and taking steps to make whatever repairs are necessary to restore the service as soon as possible.
