Gas fire protection systems are usually used to protect rooms where the items within are high value and could be destroyed if water or other agents were used to extinguish a fire, for example in an art gallery, museum, data centre, or other areas containing high value equipment.
In instances such as the above, gas is preferable as an extinguishing agent due to the need to minimise damage to the assets. A further example of where a system like this may be used is an air traffic control centre, where there not only is highly expensive equipment present, but the potential for airline disruption should the fire not be extinguished quickly and equipment be damaged.
However, the overall integrity of the system is vitally important and many factors including the design of the system, the quality of the installation, the testing of the pipes that carry the gas and the integrity of the protected room matters greatly to the overall effectiveness of the system.
The Fire Industry Association (FIA), a leader of excellence in fire safety, has released a number of guidance documents to cover critical aspects of the application of gas systems and its latest guidance document covers the process for room integrity testing. The guide covers best practice for the tests and sets out how to do the tests correctly.
The document, called ‘Guidance on Room Integrity Testing and its Interpretation’ covers the development of integrity testing, the characteristics of gas leakage, and the standards that should be referred to. In addition, the guide details and sets out both the procedures for the test, and a helpful checklist to ensure that every part of the test has been done (and done correctly).
The important thing to remember in the design of a system is that the correct quantity of gas needs to be calculated to create a concentration that will extinguish the fire.
It should be noted that apart from developing the correct initial concentration, it is important that a minimum concentration is maintained for a specified period of time (usually at least ten minutes). The concern is that if the gas leaks out and the source of the ignition is still there, the fire could reignite.
The guidance document, ‘Guidance on Room Integrity Testing and its Interpretation’ from the FIA explains:
‘All gaseous fire extinguishing systems discharge their gas into an enclosure where the turbulent gas discharge creates a homogeneous mixture of the gas in air. During this process air and some gas is expelled from the enclosure due to over-pressurisation (caused by the injection of a volume of gas).
‘The design concentration of gas in air is 30% greater than that needed to extinguish a fire. Whilst this ensures that the fire is extinguished, the gas/air mixture provides little cooling of the source of the ignition, so the concentration of gas in air needs to be retained for a period after the end of discharge, sufficient to allow the fire to cool below its auto ignition temperature. This period is referred to in the gas system standards as the ‘Hold Time’.
‘Historical note: The failure of enclosures to retain the gas/air mixture for a sufficient period lead to fires re-igniting in Halon gas protected enclosures in the 1980s. The fire protection industry initially addressed this by performing full monitored discharge tests with concentration measurements to establish hold times. However, Halon was found to be one of the gases damaging the Ozone layer so Halon was phased out and the fire industry had to find another means of determining the hold times for the gases which replaced Halon.
‘Once the discharge has been completed the enclosure returns to normal atmospheric pressure filled with the homogeneous mix of the fire extinguishing gas and air. All these gases (with the exception of nitrogen) are heavier than air so the resultant gas /air mixture is also heavier than air – thus producing a ‘Column Pressure’ – the pressure created at the base of the enclosure due to the weight of the gas/air mixture.
‘As a result, the gas/air mixture escapes through lower level leaks and vent paths in the enclosure boundary’. At the same time, air leaks into the upper part of the enclosure – replacing the volume of gas/air as it escapes. Thus, the key to determining hold time is to establish the leakage characteristic of the enclosure.’
Room Integrity Testing
Room Integrity Testing is a test that is designed to ensure that the room is sufficiently well sealed to prevent the gas from leaking out.
The test needs to be carried out every 12 months as part of a maintenance schedule. The need for remedial leak sealing is the responsibility of the client and not the fire protection contractor.
The room integrity test also referred to as the door fan test can be regarded as an MOT for the enclosure. As such it applies to the enclosure and its associated gaseous fire extinguishing system on the day the room integrity test was carried out.
However, it is necessary to ensure that the gas system continues to provide effective protection throughout the service life of the protected risk. It is therefore essential that, as part of the routine inspection and maintenance procedures that apply to the systems itself, the room integrity test and the hold time calculation is repeated annually (as required in the ISO 14520 and EN 15004 standards) unless documentary evidence exists that no changes have been made to the protected enclosure, since it’s last test.
Accuracy of the testing procedure is of a primary concern and should be the major concern of the technician.
For example, if the test is not set up correctly, this will impact the outcome of the test. Additionally, if the input of data into the integrity test modelling software is not entered accurately, the calculations will be impacted and the result will be incorrect.
To find a detailed outline of the testing procedure and to gain a helpful checklist to ensure test accuracy, download the FIA’s technical guide ‘Guidance on Room Integrity Testing and its Interpretation’ from the publications library under the ‘Resources’ tab.
Today's Guest Blogger is Alan Elder, who sits on the FIA's Extinguishing Council as an FIA Member.
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