【 Weak current College 】 gas extinguishing system security issues and strategies (part two)

The evaluation findings indicate that:
1. system security assessment theory and methods can explain gas fire extinguishing installations of security problems, and this evaluation is very meaningful.

2. in the case of the above assumptions, the installation of gas fire extinguishing installations are not very meaningful. If necessary install gas fire extinguishing installations, should take effective measures to further reduce the risk of the system.

3, reduce a risk factors of risk caused by accident, you can reduce the likelihood of an accident (that is, the probability of accidents) and reduce the severity of the accident (accident may cause loss of) these two aspects to consider.

4. gas fire extinguishing installations of security issues, reduce cylinder explosion accidents may cause losses and the probability of occurrence of technical measures do not result in a new, more dangerous, harmful factors, for reducing the use of the danger of fire extinguishing equipment is very important.

5. gas accident accidental spraying of risk than the danger of explosion of the low level, but also in the same order of magnitude. Moreover, despite gas accident accidental spraying of economic losses are relatively large, but very high probability of occurrence, impact, therefore, the same must be taken seriously.

4. improve gas extinguishing facilities security approach

That we always can cause gas fire extinguishing installations safety accident two aspects (i.e. cylinder explosion and gas mistakenly shot) to reduce the risk of the system and can increase system safety technology or approach.

First, we use the fault tree method, may arise that two accident causes and conditions. See the following figure.


Figure 1 cylinder explosion of fault tree

Diagram:

T1-single cylinder explosion X3 — pressure indicating device failure causes the initial filling pressure (or quality) ultra high

M1-cylinder pressure-relief valve failure superelevation X4

M2-cylinder wall thinning X5 — bottle medium corrosion

M3 — breakage X6 — external atmospheric corrosion

M4 — cylinder manufacturing quality ontology X7 — adjacent cylinder explosion

M5 — external heating X8 — other foreign objects impact

M6-initial filling pressure too high X9 — cylinder ontology defects

X1 — sun radiation X10 — damage later manufacturing process

X2 — flame baking

From figure a visible, there may be a cylinder explosion of four of the following reasons:

1, pressure indication unit malfunction or temperature ultra-high pressure cylinders and so, at the same time with safety valve failure.

2, due to the corrosive medium in bottles or external atmospheric corrosion caused cylinder wall of thinning.

3. external damage.

4 cylinders of quality issues.

Qualitative analysis on the basis of the above reasons, we can see that guarantee product manufacturing quality and on the use of strict management cylinders for gas fire extinguishing installations is very important. If we make sure that the product manufacturing quality, if we take effective management measures regularly in a comprehensive with steel cylinder safety testing and monitoring, to ensure that the steel cylinders and its related parts (including safety valves, etc) and always in a good state of security, timely detection and replacement of failure of the steel cylinders, you can make the cylinder explosion of the possibility or probability of much lower. But as long as the chance to drop an order of magnitude (this requirement is not to do), then the system cylinders exploding risk will drop an order of magnitude. Of course, any security precautions of use are for the price, the price reflected in increased cylinder explosion occurred. But obviously, we are here to take effective measures, in the overall economic losses were limited, therefore, it does not affect the risk level of the order of magnitude.

Constitute a cylinder explosion risk on the other hand is the explosion may cause economic loss that the severity of the accident. There is no doubt that the losses caused by the explosion would be enormous, and therefore, as far as possible to reduce the losses caused by the explosion might we use gas fire extinguishing installations must be fully aware of. From this point to consider, a large number of high pressure cylinders should not be installed in the basement of a building; in the central installation in high pressure cylinders in a closed space, you should consider the vent wall; also, you should avoid using pressure relatively high, cylinder volume relatively large gas fire extinguishing installations.

System cylinders explosion risk degree drop an order of magnitude does not mean that the overall risk of the system also corresponds to drop an order of magnitude, because as the explosion hazard levels decline, gas spray dangerous mistake for the system total influence of the degree of risk will be gradually increased up to occupy the position and decided to overcome this danger becomes increasingly important. From the above analysis we can see that decision gas accident accidental spraying of major risk factors are not the seriousness of the accident, but the probability of an accident. Therefore, reducing gas Jet accident risk of mistake should be primarily from lower accident rates. See Figure 2.

Figure 2, gas accident accidental spraying of fault tree



Diagram:

T2 — malfunction of electrical control equipment (0.1 times/year) Y3-mal by remote start button (0.013 times/year)

N1-fire alarm controller linkage of non-normal output signal (0.001 times/year) Y4-MAL press start button (0.012 times/year)

N2-Start button malfunction (0.025 times/year) Y5 — other misconduct (0.012 times/year)

N3-startup circuit (0.024 times/year)Y6-damp and other environmental reasons (0.012 times/year)

N4-control program is corrupted (0.05 times/year) Y7 — lightning interference (0.02 times/year)

Y1-first fire detector malfunction (0.01 times/year) Y8-electromagnetic interference (0.02 times/year)

Y2 — second detector malfunction (0.01 times/year) Y9-other interference (0.01 times/year)

Brackets for various events of the estimated probability

Visible from Figure 2, gas main cause of accidental spraying fire-extinguishing system is the electrical control device malfunction, which can cause electrical control equipment malfunction events have the following:

1, fire alarm control linkage of non-normal output signal;

2. Start button malfunction;

3. start line short circuit;

4. control procedures were destroyed.

In these cases, the first event of incidents and other events, are not in the same order of magnitude, so they can be ignored. While the other three events are the security measures of the direction of the main considerations, especially the fourth event of the occurrence, cause no warning of the gas may mistakenly shot and even lead to death, personal injury, accordingly, should become a prevention focus.

To sum up, safety evaluation techniques and methods of application, so that we can both qualitative and quantitative analysis of system security, but also for us how to properly take security precautions to improve system security to provide a basis. At the same time, we can see that in the evaluation of the implementation of security, the security technology methods and management measures adopted for system security impact simply correction factor of generalization, but rather to take safety measures of the system for reassessment, the result and the original system of evaluation results can be compared. That is, a system of safety evaluation, various factors in the system should be fixed, not in the evaluation process, make changes to the system, otherwise, respond to changes in system evaluation.

5. control device reform programme and its significance

We mistakenly thrown in on the gas nozzle the main cause of analysis you can see, there are four reasons why event can cause the final outcome of the event "the electrical control device malfunction", thus causing accident accidental injection. While these four causes of events (the first cause events) is "or" relationship, i.e. any one incident will result in the final outcome of the occurrence. "The electrical control device malfunction" the probability is the probability of four events.

Further analysis shows that the "fire alarm controller non-normal output signal" event linkage is composed of two "fire detectors of malfunction" event. These two events (the second level cause events) is "and" relationship, i.e. must be two fire detector malfunction events occur at the same time, is likely to trigger accidentally sprayed accident. We know that the two events simultaneously probability is the probability of their occurrence alone (0.01 times/year) of the product. This is the first level cause event (i.e. "fire alarm controller non-normal output event linkage signal") the probability of occurrence (0.001 times/year) an order of magnitude lower. This design is no fire extinguishing system design specifications are provided. This shows the specification in order to reduce the fire detector misoperation cause gas accident accidental spraying of possibility, already done a safety design. The other three events of the second level cause events are between "or" relationship, then the probability of them to throw their second level causes the probability of occurrence and, therefore, can only lead to the result increase the probability of the event.

This illustrates that raises an event occurs because the results of the event if it is the relationship between the "or", so that such an event, the more the result of the incident, the higher the odds, the results of the risk of accidents in which the; on the contrary, if a result event is composed of two or more mutual satisfaction "and" relationship of cause event is raised, the event, the more the results as well as the possibility of events by the event causing the accident, the less risk. This analysis helps to take safety precautions of the decision provides a correct way. In other words, in order to reduce a risk of accident, whilst the accident caused by the Elimination of the cause of the event causes the event or to reduce the probability of the event, but when these means are not obvious or cause events beyond question, you can design an additional reason for the event, and bring it into line with the original one or more cause events constitute phase "and" relationship, so that you can make the result event incidence is lowered. And, the attached event design in the closer the end result event causes the event layer, instead of forming phase "and" relationship of cause events more effect.

We continue to attract the gas fire extinguishing system and electrical control equipment malfunction events cause events, for example. As a result of raised "fire alarm controller linkage of non-normal output signal" event causes the event second level is the phase "and" relationship, therefore, in four of the first level of the event, this event incidence is relatively much lower. Similarly, if we in the electrical control device's original remote start button and then concatenating a launch button to make the two button press will start the fire controller, this is equivalent to the Start button raises the "wrong action" in the event of two second level cause events other than the one event, and make the additional cause events and "mal by remote start button" cause event phase "and" so that you can enable "launch button malfunction" probability of events down to 0.0122. However, throwing gas fire extinguishing system and electrical control equipment malfunction results in the event of the first level of the event has four, we use the technology if you only make one or two incidents decreased the probability ofResults of event occurrence probability is not quality. Add a remote boot button measures so that the "Start button malfunction" probability of events from 0.025 significantly reduced to 0.0122, but the end result event occurrence probability drops to only from 0.1 0.0872. Only on all-cause events are designed so that additional cause events to achieve the magnitude of the change.

Used for gas extinguishing system of electrical control equipment malfunction problems designed a secure isolation methods, to solve a variety of reasons causing malfunction of electrical control equipment, greatly reducing gas accident accidental injection. If this design used in the above example of gas fire extinguishing installations and security assessment of fault tree to describe (see Figure 3), you can clearly see that its essence is in the final results of events because the event is saved with an additional reason for the event, and that this additional cause events and subject to the "fire alarm controller non-normal output linkage signal" events other than the three causes of events "and". This allows the original as long as the "Start button malfunction" and "start circuit" or "control program is corrupted" will result in malfunction of electrical control equipment, has become one of the three who happened also must meet "security isolation device malfunction" conditions that cause a final result event occurs. Assuming that "security isolation device malfunction" occurrence probability and "mal by remote start button" event is the same, the final outcome of the occurrence probability can be reduced from 0.1 to 0.0023. This makes the instance a system error occurred gas Jet accident risk by 20 million/year-downward to 0.46 million/year.

Figure 3: control unit after reconstruction of gas accident accidental spraying of fault tree

Diagram:

T2 — malfunction of electrical control equipment (0.0023 times/year) Y4-MAL press start button (0.012 times/year)

N1-fire alarm controller linkage of non-normal output signal (0.001 times/year) Y5 — other misconduct (0.012 times/year)

N2-Start button malfunction (0.025 times/year) Y6-damp and other environmental reasons (0.012 times/year)

N3-startup circuit (0.024 times/year) Y7 — lightning interference (0.02 times/year)

N4-control program is corrupted (0.05 times/year) Y8-electromagnetic interference (0.02 times/year)

Y1-first fire detector malfunction (0.01 times/year) Y9-other interference (0.01 times/year)

Y2 — second detector malfunction (0.01 times/year), Y10-safety isolating device malfunction (0.013 times/year)

Y3-mal by remote start button (0.013 times/year)

In fact, the above modification scheme has been applied in practice. Incomplete data indicate that, in accordance with the method described above, increased isolation device for 40 sets of gas fire extinguishing system in the year successfully stopped four times for these various reasons raised gas accident, mistake-extremely obvious. effect

From a security point of view of evaluation principles, reveals our gas extinguishing system control unit of the security measures of significance, but also to establish its position in the field of system security to provide a strong theoretical basis.

VI. conclusions

In summary, use systems to measure the degree of risk, from the perspective of fire safety and setting fixed gas fire extinguishing installations, meaning for system security. Therefore, we must fully aware systems and comprehensive security and fire-extinguishing device itself and the importance of security issues. Depending on the system of safety evaluation of theory and methods, the risk of fire extinguishing equipment, mainly by cylinder explosion and gas mistakenly shot two aspects, reduce their risk of accident reduction measures should hazard severity and likelihood of reducing accidents in both directions. We should give full attention to the gas fire extinguishing equipment selection and installation conditions of pressure cylinders in order to minimize the occurrence cylinder explosion in severity, should pay attention to product manufacturing quality and enhance the safe management of pressure cylinders to reduce the incidence of the explosion. At the same time, be in safety assessment methods, under the guidance of increased incidents of all cause events of conditions of technical measures to reduce gas accident accidental spraying of probability. Only when these administrative and technical measures taken to apply to the dangers of gas fire extinguishing installations to a significant reduction to sustainable levels, gas fire extinguishing installations use is really valuable.