SHEVS – explained easily

In case of fire, smoke and heat exhaust ventilation systems save lives. We explain how SHEVS work and what they do.

Reading time: ca. 11:00 min.

Smoke and heat extraction systems save lives

Smoke and heat exhaust ventilation systems (SHEVS) are an important component of preventive fire protection. They serve to protect both human life and property. If SHEVS are planned correctly, they can limit damage from the maximum extent possible or even prevent it. Depending on the type of building, various legal principles, regulations and recommendations must be considered when dimensioning. Because only if SHEVS are selected properly for the type of building, smoke and heat ventilation systems will direct the dangerous fire smoke out of the building and save lives.

What exactly is a SHEV?

Smoke and heat exhaust ventilation systems save lives. In doing so, however, smoke and heat exhaust ventilation systems by no means prevent a fire. But in case of fire, they do have a considerable influence on limiting the damage and protecting the property. How does it work? Explained effortlessly, a smoke and heat exhaust system consists of individual smoke and heat exhaust units (SHEVs). SHEVS can be roof lights, glass skylights or opening vents in glass roofs and continuous roof lights - in short: openings in the roof surface that are integrated into skylight systems.

These open automatically or manually in case of fire, forming exhaust openings to release smoke and fire gases through the roof. In addition, a smoke and heat ventilation system can include supply air openings in the lower wall area, fire detection elements, activation or release devices, opening units, power supply lines and smoke aprons in case of larger rooms. What exactly is behind a smoke apron is explained later in this article in connection with the low-smoke layer.

SHEVS must be dimensioned in a way that all smoke and fire gases are removed as quickly as possible and cannot completely fill the room in case of fire. The primary goal is to always create a smoke-free zone on the floor. How the SHEV system must be designed and how the individual smoke exhaust units must be arranged depends on the size, type and use of the building.

How is a SHEV dimensioned?

The calculation of a SHEV is based on the Aa area (formerly Aw-). The Aa area of a SHEV (window, rooflight, skylight) is the area that may be considered aerodynamically in the fully open state - i.e. the aerodynamically effective opening area (Aa). The Aa area is defined both for a unit and for the entire system. The total effective opening area of the complete SHEV then accordingly is the sum of the effective opening areas of all the individual smoke extraction units. Smoke and heat exhaust ventilation systems can be arranged on flat roofs in the form of roof lights or continuous roof lights, glass skylights or glass roofs, or as side windows located directly below the ceiling.

How SHEVS works

The operating principle of a smoke and heat exhaust system is based on the physical principle that warm air rises. This natural smoke extraction is caused by the thermal lift that is generated by openings in the roof or façade. The openings or heat exhaust units consequently offer the possibility of keeping buildings smoke-free, at least in the lower area, during the event of a fire. This way, lives can be saved and at the same time the building structure can be thermally relieved through targeted heat dissipation.

Smoke control focuses on personal protection. The smoke-free layer created by SHEVS ensure that people in the building have sufficient visibility and enough oxygen to allow them to escape. Heat dissipation, on the other hand, is primarily about building preservation and firefighter safety during extinguishing. In both cases, natural or mechanical smoke extraction systems therefore support the following tasks in case of fire:

  • The self-rescue and external rescue of people, since people can see and breathe.
  • The inside attack of the fire department, as the fire department can see thanks to SHEVS, orientate themselves quickly, rescue and fight the fire.
  • The protection of property, since a reduction in heat exposure and smoke spread protects buildings and fittings.
  • The protection against operational failures due to far less smoke damage to buildings and systems and correspondingly faster fire damage restoration.

Escape and rescue through low-smoke layer

A SHEV is designed for the initial phase of a fire. This is the first 20 to 30 minutes until the arrival of the fire department and its first measures for rescuing people and extinguishing the fire. The smoke extraction system is planned in such a way that the smoke is layered in the room. This means that the upper area of the hall is smoked, while a layer of at least 2.50 m high above the floor remains, in which free visibility and breathable air is ensured. The layer can also be dimensioned higher, e.g. to protect goods or production facilities.

For this purpose, as much smoke is extracted from the upper third of the room as is released by the fire and in the lower third the same amount of fresh air is supplied from outside. Small rooms of less than 200 m² are usually designed without smoke extraction, as the escape and fire-fighting routes are shorter there. Rooms larger than 1600 m² are divided into smoke sections through smoke aprons, each with a maximum of 1600 m². That way, the smoke can only spread within the section under the ceiling, does not cool down too much and remains hot enough to escape upwards through the openings. In this case, only the units within the affected section are opened, namely all together from a central release station.

Not all SHEVS are the same

The generic term SHEV stands for all types of smoke and heat exhaust ventilation systems. It includes various system technologies that differ in their mode of operation and function. The following SHEVS are distinguished:

  • Natural smoke exhaust system (NRA)
  • Mechanical smoke exhaust system (MRA)
  • Smoke differential pressure systems or smoke protection pressure systems (RDA)
  • Garage smoke extraction systems
  • Elevator shaft smoke extraction
  • Stairwell smoke extraction systems
  • Heat extractors (WA)

A variety of abbreviations is used in smoke protection, all of which have different meanings. SHEVS, NRA, NRWG or MRA - as similar as the abbreviations sound, they are actually extremely diverse. This makes it all the more important to know exactly which abbreviation stands for what. We have listed and explained the most important terms for you:

SHEVS - regulations and guidelines

Smoke and heat exhaust ventilation systems are indispensable for a responsible fire protection strategy. Both for the protection of human life and for the preservation of property and building values, damage prevention and damage limitation are national and economic regulations. Legal principles and technical rules specify what needs to be considered in planning, calculation and execution. For Germany, the regulations are as follows:

State Building Code

The state building code initially sets out basic requirements, which are then specified in further regulations. For example, Section 14 of the MBO states that "Structural installations must be arranged, erected, altered and maintained in such a way that the development of fire and the spread of fire and smoke (fire spread) are prevented and, in the event of a fire, the rescue of people and animals and effective extinguishing work are possible."

The respective state building code of the federal state concerned also requires smoke outlets for stairwells in all buildings above a certain height. These include buildings in which people may be present on one or more floors at a height of more than seven meters and places of assembly. An example of this is the stairwells of special buildings where there are large numbers of people who are not familiar with the location. These can be large cultural facilities or sales outlets, for example. There, SHEV systems are mandatory and release mechanisms must be placed on each floor.

DIN 18 232

DIN 18 232 focuses on smoke and heat extraction to create low-smoke layers. It regulates the dimensioning, gives instructions for proper installation, specifies test procedures and represents the recognized state of the type.

VdS - Guideline 2098

VdS Guideline 2098 includes further recommendations for the planning and installation of smoke and heat exhaust ventilation systems and specifies additional requirements from an insurance perspective. It requires smoke and heat exhaust ventilation systems for all single-story commercial buildings and for multi-story buildings where the ceiling is also the roof structure. This guideline is particularly important. If it is not complied with, the SHEVS will not be considered in the discounting of the fire insurance premium.

Special building regulations

For buildings of a certain type or use, there are other regulations that often also contain rules on smoke extraction. These include, among others, the Industrial Building Directive, the Ordinance on Places of Assembly and the Ordinance on Places of Sale, whose scope of application is implicit in the name in each case.

Safety through maintenance

Smoke and heat exhaust systems are sensitive and safety-relevant components. For this reason, they may only be planned, installed and maintained by recognized and experienced specialist companies. Specialists in the field of smoke protection will ensure that the smoke and heat exhaust system is correctly designed and properly installed. Regular inspection and maintenance also play a major role. After all, maintenance ensures the functionality of the system.

Every six months or once a year, a VdS-approved specialist company must inspect, maintain and, if necessary, repair the system so that it is reliably and safely ready for use in case of a fire. LAMILUX, for example is a VdS-approved specialist for the safe installation and maintenance of SHEV systems. As a manufacturer of skylight systems as well as SHEV systems and their control technology, the company has all the expertise to maintain and repair the systems for natural smoke and heat extraction and their pneumatic or electrical control technology integrated in the most diverse variants of skylight systems.