Requirements for FGS systems in LNG receiving stations

Currently, at some receiving stations, the ESD and FGS systems are the same, which should not comply with relevant specifications

The fire and gas system is a safety management system designed for detecting fires and gases. It collects detection signals from fire buttons, as well as sensors for smoke, fire, combustible gases, and toxic gases located at chemical plant sites, and uses software logic to control devices such as alarm lights, alarm bells, deluge valves, foam valves, and the fresh air inlet valves of the air conditioning system. The fire protection system consists of on-site detection elements, logic controllers, actuating elements, an analog alarm panel, and an uninterruptible power supply; it also includes the common alarms for the building’s fire alarm panel and air conditioning system. When the FGS system experiences functional failures, power supply issues, or faults in the detection circuit, it will issue a fault alarm, but it will not trigger any detection alarms or the fire valves. Therefore, in the FGS system, the entire device is defined as a non-fault-safe mode.

Code for Engineering Design of Liquefied Natural Gas Reception Stations 10.1.7 The fire and combustible gas monitoring system shall be capable of detecting fires, leaks of combustible gases, as well as leaks of liquefied natural gas within the plant area of the reception station; it shall also enable the isolation of production equipment and the activation of fire-fighting equipment in the event of a fire. 10.1.8 The fire and combustible gas monitoring system shall be installed independently of the process control system and the safety instrumented system; its safety level shall not be lower than that of the safety instrumented system. When a programmable controller is used, it shall be designed in a fail-safe manner.

Code for Engineering Design of Liquefied Natural Gas Reception Stations 10.1.7 The fire and combustible gas monitoring system shall be capable of detecting fires, leaks of combustible gases, as well as leaks of liquefied natural gas within the plant area of the reception station; it shall also enable the isolation of production equipment and the activation of fire-fighting equipment in the event of a fire. 10.1.8 The fire and combustible gas monitoring system shall be installed independently of the process control system and the safety instrumented system; its safety level shall not be lower than that of the safety instrumented system. When a programmable controller is used, it shall be designed in a fail-safe manner.

FGS structure requirements: As a safety system, FGS must take into account the reliability and availability of the system; therefore, the system must employ a redundant structure. Each unit area is equipped with an independent FGS system, which communicates with its respective DCS via redundant serial communication, while also sending alarm signals to the analog alarm panels in their respective control rooms. Each FGS is equipped with redundant Ethernet interfaces, which are connected via fiber optics to a redundant FGS central switch. The HMI hosts installed at the company’s emergency response center and fire stations communicate with various FGS systems via Ethernet, displaying in real time the alarm status of each detection element and enabling centralized monitoring of the entire plant, thereby improving the ability to respond to and handle emergencies quickly and effectively

The FGS input/output circuit handles 1 analog input; the output signal from the gas detector is in the range of 4–20 mA, and it is connected directly to the system’s analog input card. This signal is then transmitted to the DCS, which enables real-time monitoring of the concentrations of flammable or toxic gases in critical areas of the facility. At the same time, it implements gas concentration over-limit alarms, open-circuit and short-circuit alarms, as well as verification status indication in logic. 2. Digital input: Since the FGS system operates in a fail-safe mode, the contact signals in the system – such as those for manual alarms, smoke detectors, temperature sensors, pressure switches, flow switches, etc. – are normally in the open position; they close only when an alarm occurs. To ensure that the aforementioned contact signals function properly when needed, the system uses an SDI (Supervised Digital Input) circuit structure to process the contact inputs; in other words, the contact switches are connected in series or parallel with resistors of specific values before being fed into the analog input card. Then, the input current is evaluated logically to determine the status of the circuit – whether it is normal, in an alarm condition, short-circuited, or open-circuited – and corresponding alarm messages are generated. 3. Digital output: The DO outputs in FGS include alarm lights, alarm horns, solenoid valves, etc. Under normal conditions, these devices are not powered; to ensure they can function properly when needed, the system uses SDO (Supervised Digital Output) cards to drive such devices. The SDO card can continuously monitor the output circuit to determine whether it is in good condition; a failure in the load of the output circuit will trigger an appropriate system alarm and indicate the faulty channel.

The FGS power supply system uses a dual-power supply configuration: one source comes from the factory’s UPS system, and the other comes from a non-UPS source. At the same time, the FGS system is equipped with a separate 24-hour backup battery to ensure that in the event of a power failure throughout the plant, the FGS system can still provide safety alarms and protection for the plant for at least 24 hours.

The FGS system alarm provides comprehensive self-diagnosis capabilities for system faults, and it has strong fault tolerance. Any fault in the system, such as system failures, power supply issues, circuit faults, or cabinet temperature alarms, can be promptly displayed on the analog alarm panels in each control room, along with audible and visual alarms. Comprehensive self-diagnosis and fault alarm functions ensure the continuous safety of the equipment in the FGS system.

The above are the general requirements for the FGS system; feel free to offer your feedback

Safety Supervision General Administration Order No. 3116 **Guiding Opinions of the Safety Supervision General Administration on Strengthening the Management of Safety Instrumented Systems in the Chemical Industry: Article 11 – The FGS system shall be an independent basic control system