Comprehensive fire safety in high buildings
Fire protection concept included. Calculation of variables difficult due to their diversity
The Grosspeter Tower in central Basel has what it takes to become a new landmark for the metropolis on the river Rhine. The building, which is almost 80 m high, will be used for a variety of purposes: 10.000 m2 will be used for offices and commercial premises, there will be a hotel as well as a multilevel underground car park. This necessarily requires especially high standards for the ventilation engineering, as well as for smoke and fire protection. An additional complication is that potential tenants for the office areas must be offered flexible layouts and variable interiors. Specifically, in case of fire, the smoke protection pressure system must be designed so that it functions reliably independently of the future internal layout, enabling a smoke-free escape route from the building.
Picture 1. New landmark on an old industrial site with high standards concerning function, architecture and environmental considerations: the Grosspeter Tower in Basel.
“Intervention smoke extraction” for underground car park
The underground car park, which has a sprinkler system, is divided into four fire/smoke extraction sections using fire protection doors. The smoke is extracted from these sections mechanically via the roof with an eightfold air exchange, using simultaneous natural air flow for fresh air replacement. The goal is “intervention smoke extraction”. This enables immediate evacuation of the users and rapid deployment of fire fighters in the central parking area.
The concept for the mechanical smoke and heat extraction systems covers the underground car park, the necessary fans, silencers and smoke extraction dampers (fresh air replacement and extract air), as well as the appropriate control system including CO and NO2 sensors and transparent warning signs. The fans shall be certified for 120 minutes at 400°C in accordance with EN 12101-3.
Picture 2. Confirmed by a smoke test: the air curtain keeps the lock zone in the basement smoke-free, despite the entrance doors being wide open.
Reliable calculation is difficult
At the heart of the fire safety concept for the tower itself is a smoke protection pressure system for the fire escape stairway with associated lock zone. Both actively maintain an overpressure. An outflow, a fire services lift and fresh air replacement via two passenger lifts round off the concept. Outflow is achieved using smoke extraction dampers in the user area, supported by a fan on the roof. Furthermore, a pressure cascade prevents smoke building back up again in the stairway.
A particular challenge in the design of the smoke protection pressure system for the Grosspeter Tower was the diverse number of variables occurring during a fire:
- cumulative leaks of the building shell, leaks via the lift doors
- the doors on the ground floor which are opened completely if there is a fire
- the pressure ratio between the user areas and the fire escape stairway.
Reiner Kelch, System and Application Manager for Smoke Protection Pressure Systems at Systemair says, “The numerous variables and their interactions make it almost impossible to calculate reliably, even using integrals. Instead, due to safety margins, orders of magnitude are generally reached which cannot be implemented, either for technical or economic reasons. This makes the practical experience of a broad-based manufacturer all the more important.
A typical example is the installation of a special air curtain at the door between the lock zone and the basement. Thanks to a differential pressure of 10 Pa, this prevents the fire escape stairways from filling with smoke if there is a fire – even though the main entrance is permanently open. This is significantly more cost-effective than installing the larger supply air fans which would otherwise be necessary.
Picture 3. A supporting roof fan is part of the Grosspeter Tower’s smoke protection pressure system concept. This enables the dimensions of the outflow ducts to be kept comparatively small.
Project: Grosspeter Tower, Basel, Switzerland
Concept: Fire safety concept for high-rise office block
Service: Mechanical smoke and heat extraction systems
Product: Type AXC 560 (F) and 1250 (F) fans, silencers, smoke extraction dampers
Planning: Gruner Gruneko AG , Basel, Switzerland
Implementation: Meier-Kopp AG, Reinach, Switzerland