Every year, all over the world, modern tall buildings of various purposes are being constructed. For each of them — according to strict regulations — it is necessary to ensure the safety of users in case of fire. In order to achieve this goal some reliable and highly effective systems may be used. The systems make it possible to control the spread of smoke and heat appropriately. It is worth noticing that in most cases the most dangerous mortal threat for people during fire in such buildings is not the fire itself but the smoke and toxic gases being created during combustion process.

Protection of multi-storey buildings

Two fundamental ways of controlling the spread of smoke and heat during fire may be distinguished:

1. Extracting smoke from the evacuation space — smoke extraction sets and systems,
2. Preventing smoke accumulation in the evacuation routes — pressure differential sets and systems.

Individual solutions vary not only in their function in a building, but also in technological measures possible to apply and guaranteed safety level:

The foundations of the pressure differential system design works are as follows:

• The Ordinance of the Minister of Infrastructure of 12 April 2002 on Technical Conditions for Buildings and their Location;
• The Ordinance of the Minister of Infrastructure of 12 March 2009 amending the Ordinance on Technical Conditions for Buildings and their Location;
• EN 12101-6:2007 — Smoke and Heat Control Systems — Specification for Pressure Differential Systems — Kits;
• ITB instruction No. 378/2002 — Designing Fire Ventilation Installation for Escape Routes in Tall and High-Rise Buildings.

Each system shall ensure, among other things, a set overpressure, specific minimum airflow velocity through open doors, non-extendible maximum force needed for opening evacuation doors.

Benefits of using pressure differential systems:

• Effective protection of the lives of people by clearing evacuation routes,
• The possibility of carrying out the rescue action by fire fighters,
• Higher level of protection of the building,
• Reliability.

How do the pressure differential systems work on the example of the Safety Way system?

The idea of the Safety Way system operation is as follows: within the staircase zones with pressure differential systems a directional controllable airflow is being created. The goal is to obtain a stable static pressure distribution in the whole staircase zone under the stack effect conditions. This can be achieved by means of precise control, in the first place, supply and exhaust air flow, and, secondly, accompanying airflow resistance. It is assumed that in order to obtain a stable static pressure distribution in the entire staircase zone it is necessary to supply the specific volume of air to the underpressure zone and to channel the right volume of air from the overpressure zone.

Nominal operational parameters of the pressure differential system

The volume and ratios of the airflows are each time determined by the SMAY engineers, who carry out calculations based on the computer analysis of a given building. Those volumes depend on the following factors: the height and location of the building, the staircase architecture and the total level of air leaks, as well as the assumed functional requirements of the pressure differential system. By superimposing the pressure distribution — which arises from the stack effect and airflow resistance — it is possible to obtain a stable static pressure distribution in the whole staircase zone. The control of the pressure gradient between individual rooms treated as evacuation routes also makes it possible to gain a directional airflow through the open evacuation doors on the storey engulfed in fire. Thanks to the Safety Way system it is therefore possible to achieve nominal operational parameters of the pressure differential system regardless of the building height.

What determines the direction of airflow generated by the safety way system?

The direction of the airflow generated by means of the Safety Way system depends on the current temperature difference between indoor air and the environment. During winter, when the ambient air temperature is lower than the air temperature in the staircase of a building with a heating system, the air is being supplied at lower storeys and channelled out at top storeys. During summer, when the ambient air temperature is higher than the air temperature in the staircase of a building with air conditioning, the air is being supplied at top storeys and channelled out at lower storeys.

The Safety Way system – fully automated solution for tall buildings

The Safety Way system has been developed as a fully automated solution for tall, high-rise, and industrial buildings, where is considerable heat gain inside connected with the execution of a technological process. The lower limit of the height of a building for using industrial systems, under Polish climatic conditions, can be determined depending on the standard chosen by a building designer:

• 30 m — for PN-EN 12101-6:2007 — Smoke and heat control systems — Part 6: Specification for pressure differential systems. Kits;
• 55 m — for ITB instruction No. 378/2002 — Designing Fire Ventilation Installation for Escape Routes in Tall and High-Rise Buildings;
• 65 m — for NFPA 92A Standard for Smoke-Control Systems Utilizing Barriers and Pressure Differences (an American standard).

The Safety Way system consists of at least two compact iSWAY-FC-R air supply units, which are placed at the outermost storeys of a building. iSWAY-FC-R air supply units are equipped with reversible axial fans, which make it possible to change the airflow direction in a staircase zone, depending on the current requirements. The Safety Way system is, by default, a channel-less solution and does not require the collective assembly of air supply shafts.

The role of additional iSWAY-FC-D air supply units in high-rise buildings

In case of high-rise buildings it may be necessary to use additional (supporting) iSWAY-FC-D air supply units, which are launched when the pressure difference between the staircase zone and the reference space falls below the preset value (usually 30 Pa). It is commonly assumed that there should be one additional air supply point in a staircase zone per each 10 to 12 storeys. It is also worth noticing that when developing the general idea of a solution the designer should assume two supply and extract points located at the lower and top storeys.

This is since it is necessary to limit the airflow velocity at the terminal members of an installation. MAC-FC regulator of ISWAY-FC-R unit sets the right direction of airflow in protected space based on currently measured temperature difference between the air in the staircase zone and the ambient air. What is important, the Safety Way system does not require any additional pressure control elements and relief openings in staircases, which may often be problematic, especially in existing buildings.

The Safety Way system is being delivered as a complete pressure differential system, optimized for using in a given building. Besides meeting requirements of valid regulations, the system, as an active solution, makes it possible to shorten considerably commissioning tests and periodic technical inspections.

The operation diagram of the Safety Way continuous flow system for two conventional seasons, winter and summer, is shown in the figures below.

Fig. 1. Stabilization of overpressure in the staircase zone in a building with a heating system during winter with the use of the Safety Way continuous flow system.

Fig. 2. Stabilization of overpressure in the staircase zone in a building with air conditioning during summer with the use of the Safety Way continuous flow system.

Fig. 3. Realization of the directional airflow through the open evacuation doors with the use of the Safety Way continuous flow system.

The Safety Way system not only makes it possible to meet the overpressure criterion, but also to maintain the required velocity and direction of airflow through the open evacuation doors. When the evacuation doors open, and therefore the pressure in the staircase zone with the overpressure protection drops, the air exhaust is being shut down. At the same time the air supply is increased up to the calculated value resulting from the staircase leaks and the dimensions of evacuation doors.