By Ron Burns

Roof ventilators definitely enjoy the ‘bad apple’ reputation in the eyes of many building owners and developers — why?

Ron Burns - Bio

This is almost one of the saddest realities of the smoke ventilation industry. In my opinion, the roof ventilator is undoubtedly the most efficient manner of getting smoke out of a single-storey building or the upper level of a multistorey building. As we explore the properties of this ventilator, the features which make it special will be identified. The first question is: what makes it the ‘bad apple’?

“There is a flood in my store.” I have attended to many such call-outs from clients. Armed with water wings and ready to rescue people being swept away by the torrent, or at least, encountering a store with water seeping through the windows, I dash off expecting hundreds of thousands of rands in damages. Unfortunately, ‘flood’ is a subjective description for a cup of water. Although I do appreciate the slipping hazard and dangers this presents to the elderly in particular, I feel that the term ‘flood’ is a more than marginal exaggeration.

There are two instances where water enters the building through the ventilator — one is when the ventilator leaks (and there are several causes for the leaking which we will explore later). The other is that the ventilator allows water into the building when deployed in a fire position. This deployment into the fire condition is the reason the ventilators are installed. There are not many objections to a ventilator being open in a fire condition and having water entering the building. The objection is to the ventilator opening when there is no fire.

“If power is required to open the ventilator in a fire condition, then the power supply to the ventilator in the field Needs to be protected.”

The most common and safest ventilator that can be used is the power-closed, spring-to-open ventilator. This ventilator opens at every opportunity. When looking at water ingress, three problems are associated with this opening mechanism. Firstly, the ventilator fails to the open position when the power is unable to get to the actuator; the term used is ‘fail safe’. The biggest cause of this is not Eskom, but lack of maintenance. Backup batteries are not maintained and therefore unable to hold their charge in a power outage and with the ventilators open.

Secondly, a false alarm from the smoke detection panel, and thirdly, electrical storms.

The power-to-close, spring-to-open ventilator provides the highest level of safety. A widespread problem experienced with this ventilator is weather. On the Highveld of South Africa, electrical storms with rain are a common occurrence. Lightning causes havoc with the power grid and many power outages occur in lightning conditions. With lightning there is rain; an open ventilator in a rain condition is definitely an undesirable feature on the roof of any building.

The other problem with roof-mounted equipment is poor manufacturing, installation, and maintenance. Any penetration through the roof needs to be adequately sealed from the ingress of water. The understanding of this principle is foreign to many installers. Many flashings are incorrectly fixed to the roof, resulting in the fixings leaking. The openings for the ventilators are too often incorrectly cut — if cut too large, then the ventilators leak. The remedy is to cut the opening in the roof smaller than the throat of the ventilator. This is a great solution to remedy the poor design of the rain channels and leaking ventilators; however, the effect on the performance of the ventilator is disastrous, rendering the smoke ventilation system inadequate. A ventilator installed with a reduced throat opening is unable to function in line with the published test data. The impact on the design results in the inability of the ventilation system to maintain the clear layer design for the building — a disaster for any smoke management system.

I can safely say I have attended over a thousand handover meetings with fire departments and engineers present — I have only ever been requested to open the ventilators for rooftop inspection of the ventilators’ installation on three occasions. I wonder how many roof openings do not match the ventilator throat openings? Poor installation of this nature renders the smoke ventilation system inadequate. This is no different from purchasing a motor vehicle branded with a 2 800cc engine and having only a 1 600cc engine installed. You can imagine the media headlines and law suits that would follow.

With the challenges and reputational damage of the ventilator understood, the features of the ventilator move this piece of equipment into a league of its own in a fire condition. Ventilators function exceptionally well in un-sprinkled buildings. The limiting temperature for a fan smoke extraction system is 300°C. Although the power supply to the fan is tested to 900°C, the fan temperature rating is either 200°C or 300°C. Smoke plume temperatures need to be taken into account when specifying the smoke extraction fan. The ventilators are tested up to 600°C, facilitating effective ventilation for a longer period of time should a building be built without a sprinkler system installed.

A system of smoke ventilators installed with power-to-close, spring-to-open actuators is not reliant on power to operate. Power is required to keep the ventilators closed. The ventilators automatically deploy when the power is no longer present. The fan systems require emergency power to operate. As with the challenges experienced by the ventilators due to lack of maintenance, similar problems are experienced with smoke extraction fan systems due to lack of maintenance. Are the electrical control panels maintained? Is the integrity of the cabling checked at each maintenance visit? When was the generator’s diesel level last checked? Buildings change constantly. When the latest piece of equipment was added to the store, an ice cream fridge as an example, was power taken from the emergency power system to prevent ice cream from melting in the event of a power outage? Was the generator load exceeded for an emergency by adding product support equipment? Was the system tested in an emergency condition running solely on emergency power at regular intervals after occupation?

Ventilator performance is self-regulating. The ‘power’ driving the smoke out the building is generated by the fire. A fan is limited to the duty of the fan: should the design require 20m3/s extraction, then the fan will provide the 20m3/s. This extraction rate is provided once the fire is detected until the fan ceases to operate. There are benefits from a high level of ventilation in the early stages of the fire. The problem occurs when the fire load is increased. An example of this is an increase in the fire load for a day or two during stock take, perhaps; a fire breaks out and the required extraction rate increases by 10%, thereby exceeding the fan system duty. So 10% seems insignificant, but we dig a little. The smoke spills into the adjacent smoke zone and a second set of fans activate. Can the emergency power system supply the additional power requirement? Will the additional requirement overload the generator and trip the generator, causing the entire system to be without power and fail? Has the inlet air been designed to provide sufficient air? Will the velocity increase along the inlet air path, above regulation requirements and encourage fire spread? A larger fire requires more smoke extraction and the system is already over-powered.

The obvious question is, how do we solve the water leaks and restore the reputation of the smoke ventilator? Industry has developed a power-closed, power-open system of controlling the ventilators. This system is misunderstood, which has resulted in many such systems being poorly specified. I always encourage the embracing of the EN 12101 code. The code is specifically written to provide the highest level of safety at the lowest cost. Unfortunately, this concept has been lost in the competitive design supply nature of the smoke ventilation industry where facts are blurred by product specifications opposed to performance specifications.

Equipment suppliers have been providing limited information on the advantages of code compliancy in lieu of product-related information to bolster their sales. The power-to-close, power-to-open system must be compared to the power-to-close, spring-to-open system. Just like a rational design requires at least the same performance as the National Building Regulations, so too should the power-to-close, power-to-open product offer an equivalent solution, if not better.

“As an industry, the challenges presented by the power-to-close, spring-to-open ventilators and their premature deployment are too vast to overcome. International standards and practices support the installation of power-to-close, power-to-open ventilation systems.”

If power is required to open the ventilator in a fire condition, then the power supply to the ventilator in the field needs to be protected.

Understanding the protection requirements was covered in the previous article. This does not mean that the electrical reticulation needs to be fire rated. I often see drawings issued at time of tender, requiring fire-rated cable reticulation to smoke ventilators in the void. This can be defended; however, why go to the expense of fire-rated cable in the void and then install the electrical control panel in the void? EN 12101 does not require fire-rated cable reticulation for power-closed, power-open ventilators, provided the activation of the ventilators is from an early warning system, such as a smoke detection system — not a sprinkler system. This is an important point. Currently, a discussion is taking place as to whether the sprinkler system is required to activate the smoke ventilation system (I shall not comment). When sprinklers are controlling the smoke ventilation system, care needs to be taken to protect the electrical reticulation to power-closed, power-open ventilators.

When using power-closed, power-open ventilators, the designer needs to continually protect, monitor, and respond to any failures in the power supply to the electrical control panel, standby power monitoring, electrical reticulation to the ventilator monitoring, and monitoring the incoming fire signal.
As an industry, the challenges presented by the power-to-close, spring-to-open ventilators and their premature deployment are too vast to overcome. International standards and practices support the installation of power-to-close, power-to-open ventilation systems. Diligence to the electrical systems and investing in the correct product are paramount. Resources on fire-rated cabling where smoke detection is installed, is unnecessary — the code defines that.

The testing of the ventilator is not a well-read subject. EN 12101 is a testing standard that ensures that the ventilator opens and ventilates in a fire condition. It is definitely not a rain test. When specifying a ventilator, ensure that a series of independent rain tests are carried out on the product. The EN 1873 code is a test standard that relates to the water resistance of products. Specifiers can channel the industry to comply with independent test standards, thereby providing their clients with equipment that performs in both fire and wet weather conditions.

Ensuring that installation methods are correct requires cooperation between the roof sheeter and the ventilation installer. Employing trained personnel cannot be overemphasised when cutting a series of 3m2 openings in a watertight roof and installing a series of horizontal blades that are designed to open and provide the highest aerodynamic efficiency. Water will enter the building so do not be surprised, unless adequate steps have been taken to ensure that the correctly tested product is installed. Time invested in the training and development of watertight flashings and installation methods will ensure leak-free installations.

Next month we will compare a ventilator solution to a fan solution for a 2 000m2 and an 8 000m2 warehouse. The cost implications will be thought-provoking.