【2026 Interlock Systems】The difference between process interlocks and safety interlocks in chemical plants

I. Core Definitions and Core Objectives 1. Process Interlocking – The “stabilizer” of the production process. Process interlocking relies on Distributed Control Systems (DCS), which are also known as Basic Process Control Systems (BPCS). It is a key control mechanism to ensure smooth production processes and stable product quality. Its core objective is to strictly keep various parameters in the production process within standard ranges, thereby preventing production disruptions, fluctuations in product quality, or equipment damage caused by process abnormalities. For example, in the temperature control of chemical reaction vessels, when the temperature inside the vessel exceeds the preset range, the process interlock quickly adjusts the cooling system or pauses the feed of materials, thereby bringing production back to normal.

2. Safety interlocks – The \"guardians\" of people and equipment. Safety interlocks include Safety Instrumented Systems (SIS) and Gas Detection and Alarm Systems (GDS); they serve as protective barriers designed to safeguard human life, the integrity of equipment, and environmental safety. Once a dangerous situation arises, it will activate immediately to cut off the source of danger and prevent accidents from occurring or spreading. For example, in petrochemical workshops, when a combustible gas detector detects a leak, the safety interlock system immediately shuts down the relevant pipeline valves, activates powerful ventilation equipment, and cuts off all potential sources of fire in the vicinity, thereby significantly reducing the risk of explosion ； If the key parameters of the process unit exceed their limits significantly, the safety interlock will also trigger an emergency shutdown procedure to protect the core equipment.

II. Differences in triggering conditions 1. Process interlock: The triggering signals for process interlocks, which serve as a response to fluctuations in production parameters, often stem from changes in the process parameters during production – such as sudden temperature changes, pressure imbalances, abnormal flow rates, or fluctuations in liquid levels that exceed set thresholds – or from sudden equipment failures or abnormalities in the control system.

II. Differences in triggering conditions 1. Process interlock: A \"response mechanism\" to fluctuations in production parameters. The triggering signals for process interlocks generally stem from changes in the process parameters during production, such as sudden temperature changes, pressure imbalances, abnormal flow rates, or fluctuations in liquid levels that exceed set thresholds, as well as sudden equipment failures or abnormalities in the control system.

2. Safety interlocks: The \"catchers\" of dangerous signals. Safety interlocks are activated primarily when safety-related parameters exceed specified limits, including excessive concentrations of combustible gases, leaks of toxic gases, alarms from flame detectors, or the pressing of emergency stop buttons. Furthermore, external sudden disasters such as earthquakes and fires can also directly activate the safety interlock system.

III. Effects of actions triggered 1. Process interlock: As a \"regulator\" of the production rhythm, when a process interlock is activated, it usually leads to partial adjustments or temporary pauses in the production process. The purpose is to eliminate abnormalities, and it does not pose any direct safety threat to personnel or equipment. For example, when the temperature of the transfer pump becomes too high, the process interlock will temporarily stop the pump from operating; it will be restarted only once the temperature returns to normal levels, thereby preventing excessive wear and damage to the equipment.

2. Safety interlocks: The \"killer\" in emergency situations, safety interlocks trigger immediate emergency measures, often resulting in the urgent shutdown of the entire production system, in order to ensure the safety of personnel and equipment to the greatest extent possible. In the event of a large-scale leak of flammable gases, the safety interlock system will quickly shut down all equipment that could lead to combustion, while simultaneously activating the ventilation system at full capacity to remove the leaked gases as fast as possible and prevent catastrophic accidents.

IV. Different requirements for system design 1. Process interlock: The \"guardian\" of production flow. Process interlock design focuses on maintaining the stability and reliability of the production process, with an emphasis on precise control of process parameters and coordinated operation among equipment. The requirements regarding its response time are relatively relaxed; it is sufficient as long as the adjustment and optimization of the production process can be completed within a reasonable time frame.

2. Safety interlocks: The \"guardians\" of safety standards. Safety interlock designs must strictly comply with international and domestic safety standards and regulations to ensure they can function swiftly and reliably in any dangerous situation. It has extremely high requirements for response time; interlock actions usually need to be completed within a few seconds or even less in order to minimize the impact of accidents.

V. Differences between maintenance and testing 1. Process interlock: The \"guardian\" of production stability. The maintenance and testing of process interlocks are primarily aimed at ensuring production stability and the proper operation of equipment. It is necessary to regularly check whether the process parameter settings are scientific and reasonable, whether the equipment is operating properly, and whether the interlock logic is accurate.