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.