Process Safety time is the minimum time the process takes to move from its condition when the initiating event occurs to its condition when it will cause consequence of concern or simply its the time between the initiating event and the consequence occurring.
Process Safety Time (PST) is the time between the occurrence of a initiating event (failure or abnormal condition) in a process and the point at which the situation becomes unsafe, potentially leading to a hazardous event. This time interval is crucial for activating safety systems to prevent accidents and protect people, equipment, and the environment.
In functional safety, PST is determined to ensure that safety measures, such as alarms, interlocks, or automated shutdowns, can respond effectively before an unsafe state is reached. Key elements include:
Event Detection: Detecting the initiating failure or abnormal condition.
Response Activation: The time taken for safety systems to activate once the failure is detected.
Safe Shutdown: Bringing the process to a safe state before the PST expires.
Knowing the PST helps engineers design and configure safety systems to respond within the critical time frame. If the safety response time exceeds the PST, the safety measure may not be effective, leading to an increased risk of a hazardous event.
Example:
Consider a scenario where cooling water to reactor jackets works as a cooling media to save the thermal run away reaction causing a potential fatality. Assume the reactor temperature increases extremely fast upon failure of cooling water pump, and will reach the unsafe condition within 5 minutes. So the process safety time is only, 5 minutes. This means that for any safeguard providing protection against this consequence from occurring it must be capable to detect,decide and act within 5 minutes of process safety time.
