Technical Information
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- Written by: Keith Norgate
- Category: Technical Information
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AEROSOL GENERATORS
The popularity of Aerosol Generators is increasing worldwide but are they being used correctly for the correct applications?
Several inspections by FSIB Fire Systems reveal installations not being installed to the national standard or to the manufacturer installation guides leading us to question their ability to correctly extinguish fires.
Total flooding agents
Aerosol generators are total flooding agents and should therefore be treated in an equivalent manner to gaseous agents. It must be ensured that the room should be properly sealed to maintain the agent for 10 minutes. This should be achieved by measuring the leakage of the room and building this into the design concentration calculation or conducting a room integrity test.
Applications
Aerosol generators can be used for the extinguishment of surface Class A and B fires. It can be used for hazards that are enclosed, or equipment that in itself is enclosed to contain the extinguishant.
There are limitations as to its use on certain fuels listed in the national standard or the supplier’s instructions.
As per SANS246:2015 aerosol generators should not be used in electronic equipment areas.
Activation
It is recommended that these units be electrically activated from a fire detection system both automatically and manually. The requirements follow those in SANS 369 and SANS 10139. The relevant safety measures must be followed.
Some units provide direct operation from a thermally activated device operated at a set temperature, fitted directly onto the generator.
Calculating the design concentration
The South African standard for aerosols SANS 15779 is based on the ISO standard but several aerosols are American and follow UL/FM guidelines and, as with gas agents, the concentration requirements differ for each country.
Unlike gas standards the aerosol standard requires the designer to refer to the manufacturer’s stated design concentrations. These differ as per the agent formula.
It is recommended for electronic risks the highest specified concentration be used.
Design concentrations of aerosol generators are not effected by altitude.
Discharge time shall not exceed 90 seconds.
Installation
Installations can consist of a single generator or a series of different sized generators to cover the required room volume.
Thermal clearance distances
Unlike other extinguishments one must provide thermal clearance distances from people and equipment. These distances vary and the supplier manual should be referenced. The casing of the aerosol can get extremely hot during discharge.
Earthing
For systems in electrical substations or switch rooms the generators shall be efficiently bonded to earth to prevent metalwork becoming electrically charged.
Labelling
Installers shall attach a metal tag onto each aerosol indicating the installation date and expiry date.
Aerosol coverage
All aerosol units have a maximum distance or area coverage and maximum or minimum height and coverage distance; these must be adhered to.
Should there be air space above a generator installed at maximum height further generators shall be installed at ceiling level to achieve the required design density.
Some units require wall mounted modules to be installed at an angle, follow the manufacturer’s instructions.
Maintenance
Aerosol generator installations should be inspected and tested every six months.
Training
It is important that installers attend supplier training on the related aerosol generators to understand the requirements for installation of the particular units as they vary in requirements.
Customers must also be trained in their care, use and operation.
Conclusion
Aerosol generators may be less costly than gas suppression systems, and easier to install but it is not a case of buy them and install them when asked for a protection system by an end user. One should consider the suitability of aerosol generators to extinguish the type of fire in question and the room environment, shape and sealing to contain the extinguishant. National standards and the supplier installation instructions should be adhered to.
Like all extinguishing agents the installer should ensure he has been trained on the products he is going to install.
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- Written by: Keith Norgate
- Category: Technical Information
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HOT TOPIC
LI-ION-BATTERIES
The big concern to all fire experts right now is what is the right detection and protection that should be used for combating lithium-ion battery fires?
Currently the published knowledge on lithium-ion battery fires and the prevention thereof is still in its infancy and a vast amount of research, proven and published, still needs to be completed. With this in mind FSIB Fire Systems would be the last place to get the correct advice, but we can pass on the knowledge we have so far.
Lithium-ion batteries are re-chargeable and have become notorious for overheating to an extent where they will self-combust. They literally transform from a standing battery to a raging fire. Lithium-ion batteries contain lithium-ions in a flammable electrolyte. They do not contain any free lithium metal.
Ways lithium-ion battery fires start:
- Internal manufacturing defects.
- Physical damage.
- Electrical abuse (overcharging, over - discharging, short circuit).
- Thermal abuse (exposure to high temperatures).
Cell failure results in a voltage drop and increasing heat release and signals the start of ‘thermal runaway’ where the fires start.
Thermal Runaway starts in a single cell before thermal propagation creates a domino effect through the adjacent cells. The thermal runaway phase exhibits increasing temperature and heat release plus venting / gassing off of flammable / toxic electrolyte.
So what fire precautions should be considered?
Containment
For small portable battery powered devices fireproof bags are available and are provided on aircraft to contain small battery fires.
As battery size increases the problems get greater, for vehicle batteries for instance the containment become problematic. Protecting the batteries from mechanical damage is their compromise.
For larger energy storage systems found in buildings fireproof rooms (90 plus minutes) should be considered possibly with air conditioning to ensure the environment is kept cool.
Fire detection
Significant visible smoke is generated once battery failure starts. Detectors sensitive to the smoke emitted by batteries may provide warning and be linked to shut down electricity, isolate the batteries and activate fire protection systems and can be used. However it is not known if this is early enough to detect the thermal run away.
Heat detection is suggested by some, but this is only giving a warning when the battery has generated the heat.
Detecting the “gassing-off period” of the battery with specially designed detectors offered by manufacturers like Xtralis appear to be the most acceptable solution on offer so far.
Detecting the impending thermal runaway and trigger shut down systems to electrically isolate the individual, or bank of, or rack of battery cells and avoiding the thermal run away turning into a full fire seems the way to go.
It is also worth noting that early detection of off gassing is most effective when the ventilation is limited / minimal, but it is often the case that air movement is used to keep batteries cool during normal charging operations. Hence, off gassing sensors need to be strategically positioned and sensitive enough to detect the first signs of off gases before they become too diluted
Fire protection
Gaseous fire extinguishing systems
No significant testing has been conducted with gaseous agents to control lithium-ion batteries and general opinion is that gas protection should be avoided for this application until further information is released.
Water mist systems, aerosol systems
As above insufficient information or testing is available for these applications
Water sprinklers
From most reports the suggested suppression method at this time is for the use of water, lots of water. FM Global has conducted tests for warehouse storage of Lithium ion batteries and has been followed by ASIB producing technical guide notes on protection of lithium ion batteries.
Conclusion
Lithium-ion batteries can develop into significant and unstoppable thermal runaway fires, so careful considered measures are required to address the hazards that these pose and the options available to manage such risks.
In all cases, a risk assessment is required to determine the nature and extent of the fire challenges and the safety measures that should be put in place.
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- Written by: Vaune Everington
- Category: Technical Information
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A CLASS LOOPS
If we loop the A leg of an addressable system to the B leg, we can fool the system when we have an open circuit or save cable on the installation by not returning the B leg.
All too often during the inspection of an addressable fire system it is discovered that the loops have been “bridged”. (As seen in the photograph).
A-class wiring is a loop, we have a start point that leads outwards from the panel following a route to a number of connected devices and returning to the same point (the fire panel) – this cable is now wired into the input of the loop.
On these systems the signal travels from both points – the ‘in’ and ‘out’ terminals, this enables the system to communicate with devices even if a section of cable becomes damaged (not all devices after this point are now disconnected, as the system is still communicating from the other direction).
We often find that people have settled to ‘fool’ the system rather than locate and repair the cable fault, they do this by bridging the loop inside the panel, the panel sees that the cable reaches from the ‘in’ terminals to the ‘out’ terminals and no longer shows a fault condition.
Problem solved?
Absolutely not!
With a cable fault on site there is a chance of devices being offline; sections of the installation may not be active without you knowing! Especially if more than one section of cabling is damaged!
The bridging of loops is unacceptable and poses a serious risk to the integrity of any addressable fire detection system!
All addressable systems are designed to give fault free operation as much as possible. With the utilisation of short circuit isolators installed at the beginning or end of every zone on all addressable loops and having the loop cable correctly installed (without bridging the in and out terminals) the system will operate with the least of disruption providing you with true information.
If you see loops installed in your addressable system, get a new service provider, or call the FSIB who will assist.
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- Written by: Keith Norgate
- Category: Technical Information
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NEW
Another first for the industry.
FSIB Fire Systems have released guide notes for fire detection and gas suppression installers.
Two handbooks free of charge specifically for fire system installers.
Another step forward in information supply in helping to uplift the industry.
Installers can log onto the FSIB website, register their details, and have access to information regarding their day to day duties, information specific to the installation of gas suppression and fire detection has been laid out in an easy to read format.
If they are unsure of how an installation has to be conducted, they can log in and search the handbooks for the information required.
Log in now to www.fireza.net to view this great new installer aide.
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- Written by: Keith Norgate
- Category: Technical Information
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Every fire system whether it is a fire detection or gas extinguishing system shall be issued with a log book.
Any system handed over to client without a log book is non-compliant to the South African Codes of practice.