Discussion on the distance between instrument cabinets and Class A and B process rooms
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Recently, I worked on a medium-sized project. When the overall layout was submitted to Anping (Zhejiang) for review, the experts suggested that the instrument cabinet rooms should be located outside the plant area, just like the control room. Otherwise, it must be designed as an explosion-resistant structure. Refer to HG20508 section 4.0.7. Even with a distance of 15 meters between them, it won’t work. But with a spacing of 15 meters, a motor control center can be installed, and explosion protection is not required! In accordance with the requirements of Table 5.2.1 in standard GB50160. It’s really hard to understand – electric MCCs involve much higher levels of risk and energy consumption compared to instrument cabinets. So why is it okay for MCCs, but not for instrument cabinets? Additionally, the on-site cabinet room does not include the SIS cabinets; those are placed in the control room together. With this change, the instrument cabinet room is located more than 500 meters away from the site; there are over 3,000 I/O points in total, which results in a truly impressive setup of cable trays: a total of 6 sets of 800mm cable trays that must pass through the plant’s ductwork in two layers, from south to north, before reaching the cabinet room! This is the first time I have encountered this in my over 20 years of working on instrument design. Since the site is an explosion-proof area with dust present, creating a poor working environment, it is not suitable to use remote I/O. It was unexpected that in a modern chemical plant, it would be impossible to achieve the intelligent factory concept that has been advocated all along; as a result, this ingenious requirement from the experts forced us to revert to designs from 20 years ago.
4.0.2 The on-site cabinet room should be located as close as possible to the process unit it serves, and must be situated outside areas prone to explosions. When it is installed in an additional structure, the floor beneath the movable floor of the on-site cabinet room should be at a higher level than the outdoor ground, with the height difference being no less than 0.6 m. 4.0.3 The on-site cabinet room should preferably be installed separately. 4.0.4 The height of the on-site cabinet room for blast-resistant structures should be one floor, and shall not exceed two floors. 4.0.5 The location of the on-site cabinet room should take into account the wiring of the device cables, in order to reasonably reduce the cable length. 4.0.6 The on-site cabinet room should be arranged according to the overall plant layout and its relationship with the central control room, either by grouping cabinets by device or production unit, or by combining multiple devices together. 4.0.7 For chemical plants with explosion hazards, the on-site cabinet rooms shall be designed with explosion-resistant structures
4 On-site cabinet rooms 4.0.7 For on-site cabinet rooms in chemical plants where there is a risk of explosion, an explosion-resistant structural design should be employed. Based on the practical experience of chemical engineering companies, explosion-resistant cabinet rooms have the following advantages: 1. Not only are there many people in the on-site cabinet room during startup and commissioning phases, but there is also a small number of personnel present there throughout normal production periods; thus, an explosion-resistant cabinet room provides better protection for human safety. 2. The control systems and safety system equipment located in the on-site cabinet room are responsible for controlling the equipment as well as ensuring safety interlocks. In the event of an explosive shock wave, an explosion-resistant cabinet room allows the equipment to shut down safely and in an orderly manner. 3. The control systems and safety system equipment in these cabinet rooms are very expensive – large-scale installations can cost millions to tens of millions of dollars – and the time required to restore them after damage is long, involving re-purchasing, integration, installation, configuration, and circuit testing. Especially in cases where certain installations use patented control systems, the restoration process takes even longer, which hinders the resumption of production. The on-site cabinet room with blast-resistant structure can prevent the control system from being damaged by explosions.
The provisions of 20508 and the explanatory notes state things very clearly. If it’s blast-resistant, then it must be blast-resistant. If one does not want to implement blast resistance measures, a blast resistance calculation can be carried out; if the calculations show that blast resistance is not necessary to meet the requirements, then it is possible to do without such measures.
Don’t say that the motor center is more important than the instruments and systems. Blaming others for looking down on the fashion design field while doing something that embarrasses oneself
The instrument cabinet room is definitely more important than the MCC; it also has emergency shelter functions, so it still needs to be designed to withstand violence
The instrument cabinet room is of high importance, and explosion resistance design is a fundamental requirement. Those who are able can move out.
500M is okay; considering either the high cost of implementing anti-riot measures on-site or the high cost of cable routing, it’s better to choose the option that is more advantageous
It is clearly stated in the guidelines that an evaluation is required. Either you go up, or not. There’s nothing left to study. Additionally, the instruments and systems are truly more important than the MCC.
I never said that MCC is more important than the instrumentation system. What I mean is, in terms of risk, higher electricity consumption and heat generation increase the likelihood of fires and explosions. In terms of personnel, both the MCC and the instrument cabinets are also unattended on normal days. The important SIS units have been installed in a control room located more than 500 meters away, so that safety measures can be taken in case of danger. The location of the MCC I’m referring to is an independent building situated 15 meters away from the production facility area, with a maximum of 2 floors; it is in a non-explosive hazard zone, so only meeting the fire separation requirements is sufficient
Actually, when our overall plan was submitted for approval, we proposed that the building between the MCC and the instrument cabinets be designed to be blast-resistant, but this proposal was still rejected – precisely because of the existence of those instrument cabinets. If an instrument cabinet room is not included, the MCC does not need to meet an explosion-proof design spacing of 15 meters. Which standard specifies this?