Equipment under control, definition

Definition of physical equipment including equipment-under-control, control systems and procedures The normal transport system has both traffic control systems and plant control systems, including ventilation in undersea tunnels... 

IFC 61508 Originally functional safety was defined as part of the overall safety relating to the equipment under control (FUC, see Clause 8.1.2), and the EUC control system which depends on the correct functioning of the E/E/PE safely-related systems, other technology safety-related systems and external risk reduction facilities. Later came the generalized definition of functional safety, which is part of the overall safety that depends on a system or equipment operating correctly in response to its inputs. Functional safety is achieved when every specified safety... 

The scope definition section requires the definition of the boundary of the process and equipment under control being assessed, together with its control system. Since in the majority of cases the input to LOPA is taken from preliminary hazard analysis or HAZOP, the scope is more or less otherwise developed from previous analysis. It is necessary to ensure that equipment under control and its environment are sufficiently understood along with scope and boundary including interface before detailed assessment commences. 

The definition of equipment under control given in the lEC standards is ... 

Maintenance of equipment under the fire prevention plan. Certain equipment is often installed in workplaces to control heat sonrces or to detect fuel leaks. An example is a temperature limit switch often found on deep-fat food fryers found in restaurants. There may be similar switches for high-temperature diptanks, or flame failure and flashback arrester devices on furnaces and similar heat-producing equipment. If these devices are not properly maintained or if they become inoperative, a definite fire hazard exists. Again, employees and supervisors should be aware of the specific type of control devices on equipment involved with combustible materials in the workplace and should make sure, through periodic inspection or... 

A more formal definition of FMS is that it consists of a group of programmable production machines integrated with automated material-handbng equipment and under the direction of a central controller to produce a variety of parts at nonuniform production rates, batch sizes, and quantities (Jha 1991). 

The rationale behind the definitions of iow demand mode and high demand or continuous mode in lEC 61508 is based on the failure behaviour of a safety-related system due to random hardware faults. Underlying much of the reasoning is the distinction between safety-functions that only operate on demand and those that operate continuously . A safety function that operates on demand has no influence until a demand arises, at which time the safety function acts to transfer the associated equipment into a safe state. A simple example of such a safety function is a high level trip on a liquid storage tank. The level of liquid in the tank is controlled in normal operation by a separate control system, but is monitored by the safety-related system. If a fault develops in the level control system that causes the level to exceed a pre-determined value, then the safety-related system closes the feed valve. With such a safety function, a hazardous event (in this case, overspill) will only occur if the safety function is in a failed state at the time a demand (resulting from a failure of the associated equipment or equipment control system) occurs. A failure of the safety function will not, of itself, lead to a hazardous event. This model is illustrated in Figure 4. 

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