Characteristics of fire protection systems examination during special technical specifications’ approval phase

. Emergency simulation during the design phase of a protection object must be carried out in the absence of design standards and the development of special technical specifications. The development of these solutions requires a comprehensive study of the protection object and high competence of the executor in fire safety issues. There is a recommendation for territorial normative and technical councils to carry out studies with specialists of profile educational and research institutions of the Ministry of Emergency Situations of Russia when considering special technical conditions. This activity can be performed by including these persons in the commission or preparing a separate opinion on a commercial basis. The study presents the peculiarities of modeling the limiting heat flux density in a fire and the development of compensating measures, taking into account the comments of specialists of an educational organization. A shopping mall for which there are no design standards for the selection of fire barriers is considered. Seven scenarios of emergency situation development related to fires were studied, and typical violations of these works were revealed. The developers' attention is drawn to the necessity of calculating the fire risk and taking into account the evacuation time of people.


Itroduction
Special Technical Conditions (STC) are developed for facilities for which there are no design standards.This type of design documentation was approved in 2008 in the Technical Regulations on Fire Safety Requirements.Over the time that this tool has been used in the design and operation of buildings and structures, major benefits have been identified, including the ability to construct facilities for which no design standards are available.Possibility to compensate deviations from fire safety norms by additional measures; extension of possibilities in design at the expense of non-execution of standard spaceplanning decisions provided in documents on fire safety.
It should be noted that designing evacuation methods without considering distance limit values is possible; calculation of fire risk in special technical conditions is a part of design documentation and has indefinite validity; in the working out of STS the planned actions of federal state fire supervision are carried out in full according to an item 6 FZ-123 [1] taking into account design decisions, replacing part of the requirements regulated by normative documents on fire safety [2]; additional technical actions introduced into the STC are subject to a single state expert review of the design documentation as part of the project [3,4].
The main disadvantages arising from the use of STC in the design are the high cost of the development and approval of the document, the additional time costs for approval, the material costs of creating and maintaining additional fire safety systems [5,6].
The reason for the development of STC is part 2 of article 78 [1], which regulates that the document is developed on condition of the absence of design norms and includes the systems of fire safety, specialized to the characteristics of the protected object [7,8].
According to the Decree of the Government of the Russian Federation from 12.04.2021№290 About the Federal State Fire Supervision to apply STC to the object of protection it is necessary to coordinate the developed technical solutions with the main state expert of the Russian Federation on the fire supervision [9,10].
Consideration of STC is carried out by the regulatory and technical councils of the main departments of the Ministry of Emergency Situations of the Russian Federation in the subjects of the Russian Federation.The experience of these departments has shown the absence in a number of territories of research and educational organizations of fire-technical profile, which could be included in the councils.On the basis of the stated above and taking into account the increased danger of such objects, EMERCOM of Russia proposes to carry out a study of STC with participation of specialists of fire-technical, research, expert institutions, as well as fire-technical educational organizations.This recommendation is presented in the form of a letter dated 05.02.2020 № IT-19-20 by the Director of the Department of Supervision and Preventive Work of EMERCOM of Russia and is based on paragraph 10 of the Administrative Regulations of EMERCOM of Russia for approval of STC on fire safety (Order № 710 dated 28.11.2011,registered in Russian Ministry of Justice, registration № 22899 on 30.12.2011).Proceeding from the presented data, educational institutions of fire-technical profile gained demand for commercial carrying out of firetechnical expertise.The conclusion as a separate document is attached to the set of consideration of the normative and technical council of the Ministry of Emergency Situations of Russia.
The aim of the study is to identify the particularities of the fire protection systems appraisal during the STC approval phase, using the example of a shopping centre under design.

Materials and methods
The technical measures proposed in the STC must ensure the protection of human life and health, material assets and ensure the safety of third parties.Regulatory and technical councils of the main departments of EMERCOM of Russia in the subjects of the Russian Federation verify the validity, sufficiency, feasibility of the proposed measures at the protection object and in the region as a whole [11].
Territorial commissions have limitations in their authority, consisting in the ability to agree only on model decisions agreed by the Chief State Inspector of the Russian Federation for Fire Supervision or one of his deputies.The list of model decisions and minutes of the meetings of the Regulatory and Technical Board are available on the official website of the Ministry of Emergency Situations of Russia [12].
By summarizing the information provided, officials of the territorial regulatory and technical councils verify the applicability of the model solutions to the specific object of protection [13].On the basis of the information provided, the specialist of the educational organisation conducting the STC review must verify the correctness of the methodologies used to assess the fire safety system and the sufficiency of the proposed typical measures.
The object for which special technical specifications have been developed is the projected block building 'Block building of a shopping centre'.Dimensions in the plan in axes 25.55x68.35m, attached to the existing building of the shopping centre "City".The projected building is separated from the existing building of the shopping centre "City" fire wall type 1 with fire resistance rating REI150.The facade of the projected building facing the petrol filling station (GFS) Fig. 1.In this example, the need for an STC is due to the lack of regulatory fire safety requirements for the selection of a fire barrier separating the shopping centre, the outdoor car park and the gas filling station (GFS).
It should be added that STC apply only to the design of the object of protection in question and must be complied with at all stages of design, construction and operation, they are technical standards that contain additional fire safety requirements to the established or nonexistent standards [14].
The requirement for the application of developed technical solutions only in the particular object arises from the calculations of heat and mass transfer in a fire, evacuation of visitors and fire protection systems [15].Scaling developed systems to similar buildings without a comprehensive study of the features does not provide the required level of reliability [16].
The following measures have been developed to protect the projected shopping centre: A draught curtain with a flow rate of at least 1 l/s per metre of curtain length along the façade of the shopping centre.On the outside of the shopping centre's façade (facing the gas station) a fire alarm system with flame detectors, a video surveillance system oriented towards the gas station and a detector system for explosive concentrations as well as a warning system for fire (emergency) in the gas station with special texts and (or) sirens are to be installed.The notification system should be started automatically from the flame detectors or detectors up to explosive concentration as well as remotely from the fire-fighting post.The fire alarms, detectors to explosive concentrations and the video surveillance system are to be transmitted in the fire station with duty personnel on duty round the clock.
In order to prevent the heat radiation in case of fire between the open parking area (the car park of the shopping centre) and the filling station, the fire protection wall of fire type 1 with fire-resistance rating REI150, not less than 2.5 m high and not less than 75 m long should be built.
In order to confirm the adequacy of the developed technical solutions, the calculation of the fire protection distances and the calculation of the fire risk for the shopping centre and the gas station are attached to the special technical conditions.The requirements for the calculation of the fire risk in two buildings with decreasing fire protection distances between them are contained in area A. 33 [17] E3S Web of Conferences 431, 02005 (2023) ITSE-2023 https://doi.org/10.1051/e3sconf/202343102005

Results and discussion
A thermal calculation was carried out to check the adequacy of the proposed measures.Based on the results of the STC examination, the developers added three additional scenarios.In the standards, the fire protection distance must guard against the spread of flames when each of the facilities burns.To achieve these goals, the following scenarios were run during the appraisal phase: scenario (in the thermal calculation) to calculate the heat flux when a vehicle burns in a car park with an analysis of the limiting radiation density propagating in the gas station; scenario (into thermal calculation) for calculating the heat flux from burning of a shopping centre with an analysis of the limiting radiation density radiated at the gas station; scenario (into heat calculation, unloading the data from the risk of gas filling stations) of gas combustion in the gas filling station with indication of the limiting heat flux density affecting the car park and the buildings of the shopping centre.
The basis for the development of the STC was the fire clearance requirements.In order to ensure the safety of visitors it was proposed to launch a warning and evacuation control system in case of fire in the shopping centre building both from the fire protection systems of the building itself and from external flame detectors or detectors of explosive concentrations.There are several evacuation options with the possibility of transmitting special texts with different contents: With a STC signal from the PPP systems in the building, all exterior exits of the shopping centre can be used for evacuation.
By STS signal from external flame detectors or detectors with explosive concentration, there is an option of evacuation via exits not facing the gas station.The emergency exit in the exterior wall facing the gas station is blocked.
The proposed detectors to explosive concentrations are needed to identify the liquefied natural gas that is used at gas stations.In a flashover fire scenario after a depressurisation of the tanks, the gas spreads over the ground surface due to its high density, "spreading" over considerable distances.In the STC scenario, when a concentration of explosive substances in the air is detected, the facade doors shown in Figure 1 are blocked and evacuation is carried out to the safe side.This technical solution enables safe evacuation and prevents possible escape of visitors into an environment filled with flammable gas [16].
The actual distance between the shopping centre to be reconstructed and the existing operator's gas station is 40.9 m.The distance between the reconstructed shopping centre and the fuel storage tank of the gas filling station is 37.6 m.The gas station is designed with underground fuel storage tanks.Delivery of fuel to the gas station is provided by a tank truck with a double-walled insulated tank.
When carrying out the expertise it is necessary to make sure that the input data, criteria for selecting the fire scenario and the calculation methodology are correct.In the example under consideration the executors used [18].The choice of methodology complies with fire safety standards.
To verify the correctness of the methodology and the conclusions drawn, seven fire development scenarios were studied.Values of incident heat flux were determined by a field model using the FDS program version 6.7.5.In the calculation of fire distances, the main value evaluated is the marginal heat flux density.In the methodology, the critical value must be multiplied by a safety factor of 0.8 to calculate the allowable heat flux density.The heat distribution process from a fire will also be affected by weather conditions and wind direction.
To account for the worst-case scenario in each of the models, the wind speed: 20 m/s, pointing towards the object of protection.Simulated burning of the shopping centre facade.In the scenario, combustion starts in the consumer electronics shop and the standard fire load "Radiomaterials; poly-(ethylene, styrene, propylene), gethinax" was used.Once the window openings are destroyed, the fire exits onto the facade and creates a heat flux affecting the gas station building.The window openings in the filling station are filled with PVC frames.The critical value required to ignite this material is 8 kW/m².If this value is reached, ignition will occur without an ignition source.Based on the safety factor, a value of 6.4 kW/m² would be acceptable.In the simulation of Scenario 2, the maximum heat flux density was 1.094 kW/m².
A comparison of the values obtained shows that there is no danger to the gas station building from the combustion of the shopping centre.
The gas station combustion scenario is more complex, with reduced fire distances to the car park.A 2.5 m high fire wall with a fire resistance rating of REI150 is provided to protect the equipment.
The simulation of an emergency situation at a filling station must take into account the fire in the building and on the filling platform.
It should be noted that 20 mm and 76 mm pipework are used in the process and each must be calculated for a depressurisation followed by combustion.Two scenarios must be considered: determination of the radius of impact of the products of combustion of the vapour-air cloud in the case of a flashover fire, a plume in the case of jet combustion.For parked vehicles, a heat flux of 6.4 kW/m² is acceptable, without a wall 7.9 kW/m², with a fire wall 1.1 kW/m².

Conclusion
Fire emergency simulation in the development of special specifications is a mandatory part of site safety assessment.The study emphasises the initial conditions for the construction of the mathematical model, the fulfilment of the criteria for selecting the worst-case scenario, the weather conditions, and the likely actions of people.During the design phase of the special technical conditions, the safety of visitors and personnel has to be proven in relation to the specific protection object.The combination of space planning, technical systems and the arrangement of people is possible in the calculation of the fire risk.A special feature of the specifications under consideration is the calculation of the heat and mass transfer in a fire to assess the sufficiency of the proposed measures.In the technical solutions for protection against a burning gas station, the facade of the shopping centre is protected by a water curtain.Mathematical modelling suggests the redundancy of this requirement due to the fact that the calculated value of heat flux does not exceed the value of 2.4 kW/m².The existing procedure for STC harmonisation at territorial level implies that only standard technical solutions should be used.
Mathematical modelling has shown a high value of marginal heat flux density per parking area, which is compensated by a Type 1 fire wall.Using a field model to describe the fire process made it possible to estimate the volumetric and spatial effects of the fire taking into account the height of the wall and the features of the parking area.The simulation conducted showed the need for a comprehensive study of STC, the positive experience of involving specialists from educational institutions of the Russian Ministry of Emergency Situations.The availability of the material base and the specialised calculation and software complexes allows the sufficiency of the technical solutions proposed in the STC to be verified.

Fig. 1 .
Fig.1.Diagram of the façade of the projected shopping centre building, facing the gas station