Figure 2.4 Simplified bowties for loss of containment Source: SIGTTO ESD Systems, second edition 2021
In the simplified bowties, it is clear that manual activation of ESD is a barrier on the right side (pushbutton 18.10.3.1). Barriers on the right are recovery barriers that are meant to mitigate the effects of the top event (loss of containment). The design of gas carriers incorporates manual ESD activation as an important aspect of the safety case.
In the above scenario, loss of containment is the point when control of the process has been lost. It is important that personnel are trained to understand the exact point when control of the process has been lost and the importance of manual ESD activation. This can reduce any hesitancy to manually activate the ESD push-button to stop work in an emergency. Figure 2.5 provides a summary of ESD and related system functions on an LNG carrier.
The application of emergency shutdown systems has been substantiated in the oilfields (oil well heads), Nuclear plants, oil and gas processing plants, steam and gas turbine power plants, chemical and petrochemical plants, boilers, geothermal industries, etc. Throughout an emergency situation, the process operations are ceased by the ESD system, hence, isolating the danger to escalate.
For example, when used in an oil well, the emergency shutdown system is in place to prevent the pressure from bursting through the wellhead if the pressure within the system exceeds a preset limit and becomes overpressured.
Similarly, the pressure inside a boiler can increase above safe levels and cause the boiler to explode. In this system, both the pressure and temperature of the steam can trigger an ESD activation when they exceed a preset value.
When used in power plants, emergency shutdown systems are triggered by a few different things. In one application, once the temperature of gas exhaust reaches an unsafe level, an ESD will shut down the turbine producing the exhaust to lower the overall temperature of the system.
Emergency shut down systems might be used for Hydrocarbon Inventories’ Isolation System (Figure 2.6). It is effective when system isolates hydrocarbon, nothing is released into the atmosphere when the pipeline is damaged.