Surge Protection for Smoke and Heat Extraction Systems

Surge Protection for Smoke and Heat Extraction Systems

Created by: Glen Zhu | Updated Date: December 12th, 2023

Surge Protection for Smoke and Heat Exhaust Ventilation (SHEV) Systems

Regulations and guidelines define the necessity of smoke and heat exhaust ventilation (SHEV) systems as a responsible fire protection strategy. Effective SHEV systems must be set up by building design and installation standards for the protection of human life and the prevention of fire proliferation.

The SHEV system plays a critical part in enhancing fire safety within buildings which can ensure escape routes remain clear of smoke during a fire and leave more time for evacuation for occupants.

Therefore, the protection for the smoke and heat venting system is taken into consideration when we perform the installation. Surge protection is typically not a primary concern in natural smoke and heat ventilation (SHEV) systems because these systems primarily rely on natural airflow mechanisms rather than electrical or electronic components.

However, if the SHEV system includes any electronically controlled components, such as automated windows, fans, or sensors, then surge protection is necessary to prevent electrical surges. In modern buildings, mechanical ventilation systems rely on incorporating automated or motorized components to operate.

Both natural smoke and heat venting systems and mechanical smoke and heat venting systems often utilize automated opening mechanisms for their vents. Surge protectors are designed for these electrical elements which are vulnerable to power surges.

The principle of SHEV system

The smoke and heat exhaust ventilation system aims to create a smoke-free layer by removing smoke to facilitate safer evacuations in the early stage of the fire.

Natural smoke extraction works on the principle of thermal lift, hot air rises due to its low density, creating a buoyancy effect that encourages smoke to move upward. Mechanical ventilation relies on the drive of powered systems, to create airflow by either exhausting smoke directly or by creating a pressure difference to guide smoke toward designated extraction points.

Figure 1 – The principle of smoke and heat exhaust ventilation systems

A mechanical fan is employed to create positive pressure in specific zones like stairwells, elevators, vestibules, or designated areas within a building. This pressure differential acts as a barrier, preventing the migration of smoke into these zones, thereby prolonging the viability of essential spaces, typically evacuation routes.

Why SHEVS?

When a fire occurs, harmful smoke and heat are the top risks to casualties. Smoke and heat venting systems contribute to life preservation, visibility improvement, and firefighting assistance.

Figure 2 – Smoke and heat without SHEVS

Figure 3 – Smoke and heat with SHEVS

It is evident that with the application of a smoke and heat exhaust ventilation system, the smoke and heat have been greatly reduced. That means when a fire occurs, the SHEVS system works to release hot smoke out and let fresh air in, evacuees leave the building from the low-smoke escape routes.

With the help of the SHEV system, the extension of response time enhances evacuation opportunities for building occupants and facilitates a more effective response from emergency services.

External lightning protection

When installing the smoke and heat venting system, building structures and locations must be taken into consideration. Smoke vents are commonly installed in the roof area where direct lightning strike is the most likely to occur. There are several ways to install an external lightning protection system.

Structure with no-metal roof

IEC 62305 has regulated embedded or protruding roof-mounted structures on structures with an external lightning protection system that must be located in the protected volume of air-termination systems.

For structures with non-metal roofs that still require external lightning protection, the lightning protection system is typically designed to provide a pathway for lightning to safely reach the ground, minimizing the risk of damage to the structure.

Equipotential bonding is built via connecting all conductors to the same electric potential. The down conductor is buried in the ground to dissipate the possible lightning (Figure 4).

Figure 4 – Domelight on a non-metal roof of a structure with external lightning protection system

Structure with metal roof

The metal roof can be used as a natural air termination system due to its electrical conductivity and ability to serve as a preferred point for lightning attachment. Equipotential bonding is not required, the metal down conductor connects to the earth for discharging voltage.

However, the thickness of the metal roof shall meet the requirement otherwise flammable materials are easily ignited to cause the fire when it was perforated by lightning. If no alternative lightning current-carrying connection exists, it is essential to interconnect the air-termination systems using conductors capable of carrying lightning current (Figure 5).

Figure 5 – Domelight on a metal roof of a structure with metal down conductor

To be more detailed, there are two types of down conductors for the different metal roofs.

The walls are constructed with an integrated lightning current-carrying steel reinforcement or a steel frame structure. The steel reinforcement must be equipped with a functional bonding conductor in a 5 m x 5 m grid, connecting at intervals of 2 m (maximum mesh size: 0.2 m x 0.2 m). This requirement applies to all walls and ceilings, excluding the base plate.

Separation distance considerations are not necessary in this situation. Metal façades, connected to the earth-termination system at 5 m intervals at the lowest point (ground), also satisfy the specified requirements.

The walls are constructed from non-conductive materials such as bricks or wood, and the down conductors are linked to the earth-termination system at intervals.

A structure featuring a metal roof and standard down conductors is considered critical (Figure 6). In the event of a lightning strike, the lightning current will be evenly dispersed among the down conductors. However, it remains essential to maintain the necessary separation distance.

In such structures, an air-termination system is recommended to deter direct lightning strikes, although it does not place the dome light of the smoke and heat extraction system in LPZ 0B. As a result, a lightning current arrester is also required (Figure 6).

Figure 6 – Domelight on a metal roof of a structure equipped with conventional arresters

Surge protection

Whether metal or non-metal roofs, every direct lightning strike increases the likelihood of a fire hazard. The fact is that lightning current arresters are insufficient to deal with direct lightning strikes to the dome lights. Consequently, surge protection devices must be mounted to prevent inductive coupling.

The surge protective devices described below are dimensioned based on a voltage of 24 DV in the mechanical smoke and heat exhaust ventilation system.

The SHEV system is equipped with smoke and heat detectors that sense the presence of smoke and heat and extract it from escape routes via windows or dome lights. Additionally, the system is often integrated with a fire alarm system, fire control panel manages the operations of the whole system.

Power supply line

Install a surge protective device at the entry point of power supply lines that provide electricity to the smoke and heat extraction system. Type 2 surge protector SLP40-275/1S+1 is mounted to protect the power supply of the system.

Sensors and detectors

Smoke and heat detectors are an integral part of early fire detection. When the plume of smoke and elevated temperatures is detected by smoke and heat detectors, the fire control panel receives the signal, and smoke vents are automatically opened to exhaust the smoke and then fresh air in.

Smoke and heat detectors are often integrated into a fire alarm system. These detectors not only activate the ventilation system but also trigger alarms, alerting building occupants to quick leave.

Wind and rain sensors help prevent false activation of opening vents by detecting adverse weather conditions. When heavy rains and strong winds, the rain and wind detector would keep vents closed against water ingress or damage to the vents.

The opening of vents is driven by motor-driver actuators or operators that can quickly and reliably open the ventilation openings, exhausting indoor smoke and heat.

The function of sensors and detectors heavily rely on signals. FRD2 series are surge protectors designed for signal transmission, the installation of FRD2 can help the signals be received timely in the condition of power surge.

In some modern buildings, the home automation system is connected with the SHEV system for the whole home management. A PoE surge protector could be installed.

Control panel

The fire control panel serves as a monitor and control component to manage the overall operation of the smoke and heat extraction system via connecting to detectors and sensors, fire alarm system, and ventilation system.

To ensure continued functionality during power outages, the fire control panel may be equipped with an emergency power backup, such as batteries. This is crucial for maintaining the operation of the SHEV system during critical situations. An additional surge protector for the DC power supply is considered to be mounted.

Installation and maintenance of SHEV system

Smoke and heat exhaust ventilation systems could be various, flat roofs in the form of roof lights or glass skylights, roofed mounted exhausted fans as well as side windows. The choice of smoke extraction system depends on building size, desirable protective level, and fire safety regulations.

Regular testing and maintenance are crucial to ensure the reliability of the system in the event of a fire. It is advisable to be serviced once a year following DIN 18232 and VdS/CEA Guideline 4020. The short intervals of cleaning and inspecting also extend the service life and efficiency of the system.

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