SIS bypass button and reset button

Bypass and reset hard buttons on the SIS system must be installed. If these physical buttons are not installed, it may prevent quick action from being taken in emergency situations, increasing safety risks. Furthermore, the absence of these hard buttons may also violate relevant safety standards and regulations. Therefore, it is recommended that bypass and reset hard buttons must be installed when setting up the SIS system. .

On the auxiliary control panel, hard buttons for bypassing and resetting are not necessary; it is preferred to use soft buttons on the SIS operation station.

I searched everywhere but couldn’t find any relevant regulations or guidelines. If anyone has relevant information, they can share it so that we can all learn from it*~

Some are definitely necessary, and there should also be protective covers to prevent accidental operations

Hard buttons are linked to operational permissions and security requirements. If it is established, there must be corresponding operating procedures ； None are set up; aside from safety audits before operation and in the event of an accident, there are few cases where \"experts\" come to determine whether such setups are necessary. .

All can be achieved by setting soft buttons on the SIS operation station! Of course, for more secure management, a hardware button can also be installed; the bypass or reset function can only be activated when both the hardware button and the software button are pressed simultaneously! For reference only

According to the current practice of experts in conducting inspections*, if one company has it, then all the others should have it as well

The emergency stop button of the Safety Instrumented System must be a \"hard switch\" on the auxiliary control panel, while buttons for non-safety interlock systems in the BPCS can be implemented as \"soft buttons\" in the DCS. This is a consensus among those working in automation fields and represents standard practice. This is also stipulated in all specifications and documents. HG/T20511-2014 \"Specifications for the Design of Signal Alarm and Safety Interlock Systems\" 4.11.1 The emergency stop buttons for non-safety interlock systems can be implemented as software buttons on the BPCS operator station, while the emergency stop buttons for safety interlock systems should be implemented as hardware buttons on the auxiliary operation panel. 4.11.4 The emergency stop button shall be a red mushroom-shaped button with a protective cover. Changhui Instruments, yunrun.com.cn. GB/T50770-2013 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\": 10.6.1 Emergency stop buttons should be installed on the auxiliary control panel. GB/T50770-2013 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\" 10.2.5 Emergency stop buttons, switches, signal alarms, etc., which are connected to the safety instrumented system, shall use hard wiring; communication methods shall not be employed. The emergency stop button should be red, the bypass switch should preferably be yellow, the confirmation button should be black, and the test button should be white. Some inspections have suggested that in addition to the auxiliary control panel, an emergency stop \"soft button\" should also be provided on the SIS operation screen for the nitration reaction emergency stop button. Let’s analyze what exactly this “soft button” does. 1. Analysis from the perspective of emergency accident handling: When an emergency occurs during production and it is necessary to shut down the process or cut off power, speed is of paramount importance; a difference of just one second can lead to completely different outcomes, especially in high-risk processes such as nitration reactions. In an emergency, the operator needs no more than one second to press the emergency stop button. However, to operate the \"soft buttons\" on the SIS screen, one first has to locate the mouse – and the time it takes to find the mouse is enough to press the buttons on the auxiliary control panel. Once the mouse is found, there are usually multiple screens on the SIS, so the operator must locate the screen on which the emergency stop button is found. After that, the button itself must be identified and clicked. To prevent accidental operations, soft buttons come with permission settings; a password such as ****** must be entered. By the time all these steps are completed, it’s often too late. In an emergency situation, the author believes that no operator would choose the “soft buttons” on the SIS screen. Then why is it still necessary to provide “soft buttons”? The author guesses that there is only one possible reason: concern that the buttons on the auxiliary control panel might fail. So, will the buttons on the auxiliary control panel really become inoperative and fail to function? First and foremost, the answer is a definite no – no such incident has occurred anywhere in the world. 2. From the perspective of button failure probability, the Safety Instrumented System (SIS) is designed for fail-safe operation. The emergency stop button installed on the auxiliary control panel remains in the closed position while the system is in operation; once pressed, the switch opens, which triggers the interlock and initiates an emergency stop. Thanks to this fail-safe design, the probability of failure is extremely low; to date, there have been no instances worldwide of emergency stop buttons failing to function. Therefore, the safety of the emergency stop button on the auxiliary control panel is universally recognized, and no assessment is required in SIL classification or verification. It is precisely due to this fail-safe design that incidents of accidental emergency shutdowns caused by the switch flashing occur frequently. The author cannot think of any scenario in which the “soft buttons” on the SIS system screen could be used. If so, it must be that the operator used the “soft button” in order to use a “soft button”. However, the use of “soft buttons” increases the likelihood of accidental stops and shutdowns. If the real concern is that a single button for \"reject action\" is unreliable, then why not set it to 1oo2 at the auxiliary control panel? Currently, the emergency stop buttons in many enterprises are implemented according to the 2oo3 principle: one button has three switch contacts, which connect to three different cards in the SIS. This is done to avoid accidental activation, not to prevent failure to activate; the risk of failure to activate with mechanical switches can be completely disregarded. Therefore, installing an emergency stop “soft button” on the SIS operation screen is not only unnecessary but also increases the risks to operational safety. Author: He Long

It depends on the requirements of the HAZOP analysis report; it is not necessarily required. If a bypass is required in the HAZOP, a hard button must be installed ； As for resetting, it can be done through a soft button, a hard button, or a combination of both.