A fire scenario is treated by a large part of the participants in the process of defining fire protection conditions for a given facility as a description of the principles of operation of the fire alarm system and possibly other fire automation components / installations. There is also an attempt to assume that the development of a fire scenario should be closely related to the occurrence of a fire alarm system. Apparently, for objects not equipped with a similar system, this was not justified. In my opinion, this is the wrong approach.
In accordance with the provisions of the Polish Standard PN-EN 1991-1-2 “Eurocode 1: Actions on structures. Part 1-2: General actions. Actions on structures exposed to fire. “
Basic fire safety requirements should be implemented in accordance with the strategies adopted in the fire scenarios that also include the methods of passive and / or active fire protection.
This standard also adopts a definition of a fire scenario that should describe the course of a fire by providing key events that characterize it and distinguish it from other possible fires.
It should also be mentioned that the above standard is also referred to in the Regulation of the Minister of Infrastructure of April 12, 2002 on the technical conditions and location to be met by buildings (consolidated text of the Journal of Laws of 2019, item 1065). It does not constitute grounds for its obligatory application, however, it should be treated as the basis of the legislator’s expectations in a given scope.
I refer to this not often read standard, because the above provisions contain the essence and purpose of developing a fire scenario, i.e. identification of hazards and description of their possible course.
It is not an engineering thesis supported by a large number of complex formulas, but an engineering qualitative description of the causes and development of a given event.
It has been established that the key parameters describing fire hazards are:
- The method of using the facility, including the participation of people,
- The height of the object and its area,
- Fire load density for production and storage facilities.
The first two points are indisputable, while the fire load density parameter tells us very little about the real fire hazards occurring in the facility, as it does not take into account the following parameters:
• Minimum ignition energy – the ability to ignite a flammable material (there are substances that ignite by anything, but there are also those whose ignition may be the result of very gross negligence, intentional action or other fire, but is not possible during normal operation in a given facility),
• Fire course / development – there are substances that for a long time mainly smolder (e.g. modern wiring insulation), while others immediately after ignition take the form of high-energy fire (e.g. most flammable liquids and gases)
• Burning rate of combustible material – this is a key value, because e.g. the fire of paper stored in vertically standing rolls has a very dynamic course, while the fire of the same paper stored in piles / reams is much slower (in the PN-B-02852 standard it’s of no importance, although it is peculiar that paper stored in rolls was considered less dangerous than in reams),
• Reaction to fire – some materials smoke strongly, while others emit toxic substances …
All these parameters have a great influence on:
- the level of threats to people, rescuers and property / neighboring facilities,
- evacuation conditions,
- rules for the selection of fire protection,
- proceeding in case of fire (people), fire protection systems, other installations and devices,
- loss risk assessment.
Objectives / scope
Therefore, a fire scenario that will fulfill its function should consist of:
- Identification of individual fire hazards for a given facility with a description of the reasons for their occurrence, ignition and course, including impact on people, structure and property – it is necessary to adopt appropriate security and safety procedures, e.g .:
- The probability of fire of a given flammable material with a specific method of use may be at a negligible level, for example, stored PVC in the form of plates or powder cannot be set on fire without breaking the fire safety rules defined in Polish law. This results in a lack of justification of e.g. fire extinguishing systems, even at very high fire load density values.
- In the case of fires with very rapid development, the T1 and T2 times should be reduced to a minimum, as this may significantly increase the losses. As a result, the reorganization of safety procedures and evacuation conditions is possible.
- Selection of active (technical) and passive protections – it happens that the given protections compensate each other or are not adjusted to the hazards, e.g .:
- It does not make sense to monitor a room where the main hazards are determined by flammable gases by means of smoke detection, because the gases do not smoke, and such situations do take place.
- In the case of a room protected over its entire surface with a permanent water extinguishing device, especially with a self-activated sprinkler, protection with a smoke exhaust system is often unnecessary, because the water during the firefighting action perfectly binds the smoke and the only thing that can be justified later is ventilation after the firefighting operation, but the requirements for such installations are easier to obtain than for a smoke exhaust system.
- Rules of conduct in the event of fire – the main goal of developing a fire scenario, which should be the result of the above points. These procedures should include:
- Alerting rules with responsibilities assigned to personnel / specific functions.
- Rules for alerting the National Fire Service and other services.
- List of changes in the operation of systems / installations / devices resulting from the detection of a fire in a given area – their activation, turning off devices, closing valves or shut-off flaps, opening smoke flaps, bringing elevators to a safe level …
- The method of conducting the firefighting action.
- Evacuation conditions – resulting from the rules of conduct in the event of fire should include:
- Description of the evacuation conditions, including escape routes, their length and directions, and the location of the assembly point.
- Verification of evacuation conditions with the adopted rules of conduct in the event of a fire.
- Selection and arrangement of handheld firefighting equipment.
- Work algorithm of technical fire protection systemsand building installations – in the form of an event matrix.
When and by whom the fire scenario is developed
The scenario is a design concept and should be developed at an early stage of design, preferably after the initial arrangement of the facility and defining the use of individual rooms.
Due to the implementation at such an early stage, several subsequent versions of the document should be planned, caused by changes in the arrangement of the facility, selection of technical solutions and discussion with other participants in the design process.
The author of the scenario should be the person defining the fire and explosion hazards in the facility, however, this document should be reviewed by other participants in the design phase, starting from the contracting authority, through the architect, building structure designer and ending with designers of water installations, HVAC, electrical and telecommunication designers. Technological facilities should also be inspected by technologists, as very often some interference in the technological process is necessary.
The fire scenario should be one of the bases for the execution of executive documentation, and not the other way around, as sometimes happens.
A fire scenario is often adopted in two phases, i.e. a preliminary / simplified version is first developed for inter-industry agreement at an early stage of the design (it may be part of a larger fire safety concept), which is then developed when the other industries’ executive documentation becomes available. The fire scenario is also an excellent document for agreeing on the conditions of fire protection. with offices (e.g. the National Fire Service), the insurer and