Features of design and installation of modern volumetric gas fire extinguishing systems.
Features of design and installation of modern volumetric gas fire extinguishing systems
The principles of constructing autonomous local gas fire extinguishing systems considered in the publication are capable of adequately satisfying the needs associated, first of all, with the organization of proper fire protection of both small isolated rooms (server rooms, storage facilities, etc.) and individual functional modules containing a significant fire load (electrical cabinets, switching racks, control panels, etc.).
Such systems, due to the relative simplicity of installation, minimal labor costs for design, maintenance, as well as moderate financial and operational costs, occupy a stable consumer niche in the market of technical means of ensuring fire safety. Unfortunately, the above-mentioned approaches to the formation of fire protection boundaries, based on the installation of autonomous local gas fire extinguishing systems, seem to be most relevant only for small-volume premises or other closed objects with relatively small mass and size characteristics, possessing reasonable leakage parameters.
The issue of ensuring effective and reliable fire protection for facilities with extended linear dimensions and significant internal volume, where the use of traditional automatic water, foam or powder fire extinguishing systems is not possible for a number of regulatory, operational or technological reasons, must be resolved using automatic volumetric gas fire extinguishing systems (AVGFS).
In the modern Russian market of volumetric gas fire extinguishing equipment, services for their design, delivery, installation, repair and maintenance are provided by numerous companies and organizations, some of which have a well-deserved reputation and enjoy a reputation as reliable business partners. This circumstance must be emphasized, since AUGPT are rightfully considered to be among the most labor-intensive and expensive, requiring increased attention at each stage — from making a competent design decision to scrupulous compliance with the requirements of the technical regulations for operation. In these circumstances, the choice of an organization capable of solving this range of issues in a comprehensive manner and at a high technical level will play a particularly important role for a potential customer. Attempts to save money (this factor is usually put at the forefront) at any stage (from the stage of choosing equipment to subjective preferences in favor of a particular installation organization) in this case can play the role of a time bomb, which can manifest itself in the most unexpected way in the future.
In this case, we are talking about the adverse consequences of the activation of the AUGPT, both in normal and abnormal modes. In the event of a false alarm due to both objective (technical malfunction) and subjective (the notorious «human factor») reasons, at a minimum, the gas fire extinguishing agent (GFEA), which can be very expensive, especially in the case of using modern ozone-depleting freons in the AUGPT, will be irretrievably lost. In the most unfavorable case, there may be a threat to the health and life of people and other biological objects that did not have time or were unable to leave the GFEA zone of action. Unfortunately, in a number of obsolete AUGPT, currently forced to operate at facilities of various functional purposes, GFEA modifications may still be used, which are a source of immediate, including toxicological, danger.
Since the principle of gas fire extinguishing is to replace oxygen, which acts as an oxidizer, with inert GFFS in the shortest possible time, an environment unsuitable for breathing can form in a very short period of time. The tragic events of recent times that occurred on a ship of the Russian submarine fleet and in one of the Moscow region financial institutions (widely covered in the media) and were accompanied by fatalities as a result of the activation of gas fire extinguishing systems, even without analyzing the causes, force us to take the selection and operation of AUGPT as a whole very seriously.
It should be noted that the greatest effect from the AUGPT activity can be achieved when it is integrated into complex fire protection systems. Such systems, as a rule, include automatic fire alarm (AFA), evacuation control and fire alarm systems (ECAS), smoke removal (SRE), and other installations for controlling the engineering equipment of the protected facility. Depending on the design and organizational decisions, at least one of them can issue an incentive signal for operation (including a false one). As a rule, this role is played by the AFA control devices or forced manual start. Taking into account the fact that the installation and operation of fire protection systems is not always carried out by specialists from one organization who thoroughly know the features of the functioning and interaction of the above systems, but by employees of related contracting organizations, the probability of adverse events (unauthorized (accidental) operation of the AUGPT) remains very high.
In order to minimize the likelihood of potential direct and indirect damage from the operation (non-operation, untimely operation) of the UGPT, it is necessary to carry out all stages of commissioning of these installations with particular care. Especially many errors can occur at the initial stage of design due to underestimation of a number of key regulatory requirements of the current legislation, negligence and superficiality in the analysis of the characteristics of the protected object and the specific technical characteristics of the equipment used.
The most characteristic and typical shortcomings, quite often encountered in design solutions, mainly include the following:
— An incorrect assessment of the flammable load volume is made in each specific case, therefore, an error occurs in the selection of the standard fire extinguishing concentration, the required estimated amount of the main and reserve amount of GFTS. Taking into account the fact that in the process of current economic activity of the facility personnel, additional differentiation of the flammable load is possible, the efficiency of the AGPT response cannot be overestimated.
— It is envisaged that the tanks (batteries, modules) of the UGPT will be filled with the calculated amount of GFFS, which does not correspond to their operational and technical characteristics. In this case, we are talking, as a rule, about ignoring the volume of the gas * displacer and taking into account the filling of the tanks only with the GFFS itself. This inevitably leads to an incorrect reduction in the number of tanks themselves, which may please the customer (reduction in metal consumption, saving financial resources), but may negatively affect the operability of the UGPT, not ensuring the standard time of supply of GFFS to the protected volume. When using freons as GFFS, which are liquefied gases, the absence of a displacer gas in the cylinder (module) must be taken into account in the design solutions by including weighing devices for technical control of the mass of GFFS in the UGPT, which does not always happen in practice.
— The layout of nozzles for the release of GFFS is formed without taking into account their technical characteristics, features and specifics of the layout of the premises, due to which local zones may arise in which the standard concentration of GFFS cannot be achieved. When choosing connecting units for supply pipelines, preference is given to standard water fittings designed for significantly lower working water pressure compared to gas mains, which is unacceptable.
— Often, the hydraulic parameters of the AGPT are calculated incorrectly, and in the most extreme cases, they are not calculated at all. This circumstance is largely due to the lack of intelligible methods and clear calculation programs in regulatory documents, with the exception of the simplest options (in the case when low-pressure carbon dioxide acts as a GFFS). In these conditions, a specialist in a design organization is forced to rely solely on his subjective preferences, intuition and practical experience. As a result, a number of key parameters (diameters of feeder pipelines, technical characteristics of nozzles, etc.) are indicated very approximately, which creates additional difficulties in choosing the optimal configuration of the entire gas fire extinguishing system.
— No adjustments are made to design solutions related to the specifics of the operation of the UGPT in fire-hazardous areas. I would especially like to note the dismissive attitude to technical requirements for the proper execution of grounding circuits and the selection of electrical devices and equipment included in the UGPT, which have the appropriate degrees of protection and design options;
— When designing complex fire protection systems, incorrect data on the number and locations of fire detectors are used as a basis, which reduces the probability of timely detection of a fire source and generation of a control signal for the operation of the AUGPT. Unfortunately, in a number of cases, the need to install external optical indication devices (VOD) and loop control devices (UKSh) is ignored in the case of placing fire detectors in closed spaces.
— The optimal choice of the control panel (CPC) responsible for the correct control of fire detection and fire extinguishing systems is not always made. In the most common variants, a serial CPC is taken as the base, due to its design features, it does not provide protection for several independent spaces located within one room (raised floor, suspended ceiling), which must be controlled by a separate alarm loop, or addressable fire detectors must be taken as a basis.
— The choice of switching circuits for connecting actuators and technological units of the AUGPTS to the control panel is not always technically correct. As an example, we can point to the widespread practice of forcing the simultaneous start of several modules connected in parallel to the battery from an electrical signal coming from the control panel. In this case, there will be no constant monitoring of the start circuits of each specific module, which is unacceptable.
— There is negligence in calculating the time of safe evacuation of personnel and other persons from the protected premises before the AUPT is triggered. This circumstance is one of the most critical due to the potential severity of possible consequences, which has already been mentioned above. Of course, within the framework of one small publication it is impossible to exhaustively describe all the flaws and shortcomings encountered in design solutions, since this topic is very extensive and diverse.
Imperfection of the legislative and regulatory framework, the appearance of more advanced devices on the fire protection market, the diversity of GOTV, the conservatism of some “old school” specialists and their reluctance to deviate from previously developed standard solutions, inconsistency in the interaction of various contractors involved in organizing fire protection of the facility, the strict financial framework in which, as a rule, the customer constantly finds itself… These and many other reasons and circumstances, not being taken into account as much as possible at the stage of developing the design solution, merging together at the final stage of putting the AUGPT into operation, can have the most unfavorable effect on the state of fire protection of the facility in the future.
I would like to draw the attention of specialists of design organizations to the problem concerning the selection of containers (cylinders, modules) for storing GFFS. As a rule, traditionally, containers manufactured using traditional but outdated methods are selected as base containers. First of all, we are talking about thick-walled steel cylinders, which, due to a number of technological features, have non-uniform wall thickness, hidden defects (cavities, microcracks, etc.), which is aggravated by potential problems due to metal corrosion.
It is also necessary to focus on optimizing the shut-off and starting device (SWD), which is an integral part of the GFFS storage and release system, since the AGPT is in standby mode for almost its entire service life (if there is no normal or abnormal operation) for many years. Under such conditions, all mechanical units and kinematic mechanisms (springs, pistons, levers, etc.), as well as the starting elements of the SWD (electromagnets, pyropatrons) are inevitably subject to fatigue and strength aging processes, are subject to corrosion, contamination, souring, etc.
All of the above processes, both individually and in combination, can have the most unfavorable effect on the reliability of the UGPT operation as a whole, and the probability of these events occurring is higher the longer this system is in operation. In addition, it is necessary to organize additional labor-intensive measures for technical and routine maintenance of all modules included in the UGPT in order to eliminate or minimize these design flaws.
Currently, Russian companies produce certified cylinders made of high-strength alloy steel of high homogeneity with an internal protective coating, as well as improved design ZPUs that meet the highest requirements for long-term storage of GFTS and its proper release when the AGPT is triggered. These new products and serially produced samples are actively exhibited by manufacturers and suppliers at regularly held thematic exhibition events, information about them is posted in specialized publications and on company websites.
We would like to hope that in their daily practice, specialists from design organizations and all interested parties will take into account the mistakes made in the projects of their colleagues*predecessors, as well as take into account new products on the market of technical means of ensuring fire safety that have stood the test of time and significantly increase the reliability of the AGPT as a whole. The choice is yours and we wish it to be successful!
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O. Dyuzhakov
Director of Promo-Consulting
Source: magazine «Algorithm of security» No. 1, 2011