Guidance on room integrity testing and its interpretation

Transcription

1 Guidance Note Guidance on room integrity testing and its interpretation

2 Guidance on room integrity testing and its interpretation 1. SCOPE INTRODUCTION AND BACKGROUND DEVELOPMENT OF INTEGRITY TESTING ENCLOSURE LEAKAGE CHARACTERISTICS STANDARDS FAN TEST PROCEDURE... 6 ANNEX A... 6 FAN TEST CHECK LIST... 6 ENCLOSURE GASEOUS SYSTEM FAN TEST PREPARATION CONDUCT FAN TEST CALCULATE ENCLOSURE LEAKAGE CALCULATE HOLD TIME ACTIONS HOLD TIME PASS ACTIONS HOLD TIME FAIL of 12

3 1. SCOPE This FIA guidance paper provides guidance and understanding on what is tested, how this is done and how to improve the outcome and achieve an acceptable result in relation to the door fan test. Note: Door Fan Test, Fan Test, and Room Integrity Test are used interchangeably within the industry. This document uses the term Door Fan Test. 2. INTRODUCTION AND BACKGROUND 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 but the injection of the volume of gas). The concentration of gas in air is at 30% greater than that needed to extinguish 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 ignition source 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 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 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 mixing of 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. Annex A provides a check list of the steps to be taken in carrying out a door fan test Development of integrity Testing The energy conservation industry was, at the time of the Halon problem, already using variable speed fans to quantify the leaks in buildings for heat retention calculations so research was undertaken to seek correlations between enclosure leakage areas and the rate of loss of gas/air mixtures. The research showed that enclosure leak at different rates depending on: 3 of 12

4 The area of the openings The height of the openings The shape of the openings 2.2. Enclosure leakage characteristics Thus, it was determined that every enclosure had its own unique leakage characteristic which took the form: Q = C x Pn Where: Q = flow in litres /sec C = flow coefficient litres / sec P = column pressure pascals n = flow exponent These graphs are produced by taking a series of fan flow readings vs corresponding room pressures. Typically, the room pressures range from 10 to 60pa. This range is chosen because the upper limit is below that at which over pressure vents open and the lower one is above the pressure at which readings become unstable. The tests are carried out using pressurisation of the enclosure and repeated by depressurising the enclosure. The reason is that the pressurisation characteristic relates to the gas/air mixture flowing out, and the depressurisation characteristic relates to the air flowing in. It is usual to find that the two characteristics are different. The original research assumed that the gas/air mixture leaked from an enclosure similar to water draining from a tank, whereby the gas/air mixture was at the initial concentration where the mixture was present, and pure air above. This was referred to as sharp descending interface and used for the European and international standards. 4 of 12

5 Subsequent research found that, above the homogeneous layer, there formed a series of band layers of steadily decreasing gas concentration, which expended as the homogeneous layer descended. This was referred to as wide descending interface and used for the 2006 versions of the standards. It was also recognised that, in some enclosures, recirculating fans were not shut down prior to gas release and so continued to run providing continuous mixing of the gas and air in the enclosure. As a result, no descending interface is formed. 3. STANDARDS When the International Standards Organisation (ISO) formed its technical Committee to develop a standard for Gaseous Fire Extinguishing Systems Physical Properties and System Design, it chose the UK design guide (DD233) as its base document, which included a protocol for door fan testing and hold time modelling. This subsequently resulted in the publication of ISO Part 1 General Requirements with Annex E door fan test for determining minimum hold time. This was, in turn, adopted as the European standard EN with Annex C detailing the door fan test. (Both these were published in UK with BS prefixed i.e. BS ISO and BS EN ). In the 2000 editions of the ISO standard, the hold time pass criteria was for the extinguishing concentration at the height of the highest hazard in the enclosure. In the 2006 edition of the ISO standard and the 2008 edition of the EN standard this changed to 85% of the design concentration at 90% of the room height. This has changed again as, with both ISO and CEN agreeing to change to 85% of the design concentration at the height of highest hazard. This information is important because systems/enclosures are re-tested against the criteria which applied at the time the system was originally designed, installed, and the enclosure door fan tested. These annexes describe how the door fan test should be carried out but then provide the formulae to calculate the hold times under either descending interface or continuous mixing conditions. The gas/air mixture leaks out at its fastest rate when the leaks are equally divided between the top and the bottom of the enclosure. The ISO and EN standards provide formulae for both standard and non standard enclosures. Standard enclosures are those with a uniform horizontal cross sectional area and horizontal upper and lower boundaries. Non standard enclosures are those with a non uniform cross sectional area and non horizontal upper and/or lower cross sectional boundaries e.g. a room with a pitched roof. 5 of 12

6 The standards refer to this as an enclosure with a lower leakage fraction (the area of lower leaks divided by the total leakage area) of 0.5. As this produces the shortest hold time, the standards require that the initial hold time calculations are done on this assumption. If a pass is achieved no further action is required. However, if the required hold time is not achieved then remedial leak sealing is required. The door fan test can be useful in tracing leaks by pressurising the enclosure and using a smoke generator and following the smoke flows. Alternatively, ultrasonic leak detection may be used. Leaks should be sealed and the enclosure door fan test repeated. The need for remedial leak sealing is the responsibility of the client and not the fire protection contractor. The ISO and EN door fan test Annexes do allow for the door fan test engineer to measure/quantify upper/lower leakage areas to calculate a more accurate lower leakage fraction and to re-run the hold time calculation on this basis. Where the leakage areas are not equally split between upper and lower, the smaller openings will control the flow of the gas/air mixture and air at a slower rate than that for equal areas. 4. DOOR FAN TEST PROCEDURE a. Part 1 The doorway selected for the equipment will need to be open for the duration of the test, although it will be blocked off by an adjustable door frame. After carrying the equipment to the test enclosure, it is anticipated that the equipment set up will take approximately 1 hour. During this period, personnel would be free to walk in and out of the enclosure through any of the other entrances. A adjustable door frame (screen) is placed in the selected doorway/opening and a calibrated variable speed fan mounted in the screen opening, initially with the fan airway blanked off. Part of the set up involves running a small-bore flexible plastic tube from the protected enclosure to a reference area. (Usually this can be done in the room adjacent to the area under test). 6 of 12

7 After equipment set up, preparations for the actual test need to be finalised. This may involve opening and closing the other doors as required for the test. Signs should be posted to warn that the enclosure doors and associated doors are not to be opened/closed. Checks need to be made to ensure return air paths are open so that air that is venting from the enclosure during the tests flows back to the fan inlet so that no pressure differential exists between the fan inlet and enclosures adjacent to the protected enclosure. This may also require temporary removal of floor and ceiling tiles for the duration of the tests. 7 of 12

8 Prior to taking any readings, ensure all leakage areas are in the hold time condition by visual checking including the door closure or other opening selected for mounting the door fan. All air handling equipment that is expected to be shut down upon gas release must be shut down. At the very least, all air inlets and exhausts should be closed so that only fully re-circulating air is present. Readings of Bias Pressure will then be taken this is the pressure differential between the inside and outside of the enclosure with the fan unit sealed. The fan test readings are adjusted to take into account this pre-test pressure differential (This step will normally take 20 minutes.) Record the air temperatures inside and outside the enclosure (adjacent to the fan), and the local barometric pressure (these are required for the hold time calculations). However, if the bias pressure exceeds 3 Pa then remedial action is needed. The next step will require power to the fan equipment (120V or 240V A.C.). The fan is switched on, and varying quantities of air are blown into the protected enclosure to create positive pressures within the enclosure (These pressures will normally be in the range of pa). The quantity of air required to develop these pressures is recorded. Typically, 5 pressure stages should be taken to establish an accurate leakage characteristic. The fan should then be reversed and the tubing re-arranged for depressurization as below. In a reasonably well sealed enclosure, all readings will be completed in approximately 30 minutes (from the time the fresh air make-up is shut down). 8 of 12

9 b. Part 2 Following completion of the testing, the readings taken are entered into a computer along with details of the gas system, and the protected enclosure height and volume. The accuracy of the leakage characteristics should be checked i.e. the Correlation Coefficient should be better than A calculation of the predicted hold time at a required height is then carried out. A written report of the door fan test and the results and calculations should be provided. A typical report is provided at the end of this document. The enclosure should be provided with labels stating the date on which the door fan test was carried out. For larger and/or more leaky enclosures, two or more fans may be required to determine the leakage characteristics. c. Equivalent Leakage Area (E.L.A) The door fan test equipment and program are able to calculate the Equivalent Leakage Area of the enclosure. If all the leak paths in the enclosure boundary were consolidated into one hole this would be its area. This information can be used when determining the lower leakage fraction, and may also be used for overpressure vent area considerations. (See the FIA Guidance on the pressure relief and post discharge venting of enclosures protected by gaseous fire-fighting systems). N.B.: ISO definition of lower leakage fraction is: lower leakage fraction; effective leakage area of lower leaks divided by effective leakage area of all leaks d. Annual Re-testing The door fan test can be regarded as the gas system MOT for the enclosure. As such it applies to the enclosure and its associated gaseous fire extinguishing system on the day the door fan 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, the fan test and the hold time calculation is repeated annually (as required in ISO and EN standards) unless documentary evidence exists that no changes have been made to the protected enclosure. e. Remedial leak sealing Where an enclosure fails the door fan test, remedial sealing may be required. This may or may not be included in the scope of work of the organisation performing the door fan test. Where this is excluded, the test engineer may affect temporary seals as a means of establishing and quantifying the effects of leak paths; this for example may be by taping a sheet of paper over an open damper or grille or applying tape over the gaps around door openings. Any such temporary seals used to verify the effects of such openings must not be relied on as a permanent solution and must be removed for the final door fan test. 9 of 12

10 ANNEX A FAN TEST CONTRACTOR CHECK LIST Enclosure Enclosure name Measure enclosure height/volume Measure height of interest Ventilation shut down Y/N Temperature Leakage area of door used for test Gaseous System Agent type/quantity Design concentration System design continual mixing or descending interface Date of system installation or most recent modification British/International standard which system is designed to Standard or nonstandard enclosure equation Fan Test Preparation Equipment check/calibration Verify damper status open/closed Establish return air paths from leak openings back to the fan inlet (lift floor/ceiling tiles if required) Erect test signage (fan test in progress-do not enter) Mount fan test screen and fan in enclosure opening Replicate leakage area of test doorway Record temperature in enclosure and fan air inlet Record barometric pressure Measure bias pressures Conduct Fan Test Carry out pressurisation tests recording fan flows and enclosure pressures Carry out de-pressurisation tests recording fan flows and enclosure pressures 10 of 12

11 Calculate Enclosure Leakage Input enclosure name, date, and name of test engineer Input pressurisation test data fan flows and enclosure pressures Input de-pressurisation test data fan flows and enclosure pressures Input bias pressures Input barometric pressure Input temperatures within enclosure and at the fan inlet. Input standard or nonstandard enclosure classification Calculate enclosure pressurization leakage characteristic Calculate enclosure de-pressurization leakage characteristic Calculate average enclosure leakage characteristic Calculate Equivalent leakage Area (ELA) Check n value is between 0.5 and 1 Check correlation coefficients are above 0.99 Calculate Hold Time Input enclosure name, date, and name of test engineer Input agent type/quantity Input design concentration Input system design continual mixing or descending interface Input date of system installation or most recent modification Input required hold time Input F (Lower Leakage Fraction = 0.5 for initial calculation) Input height of interest Input system design continual mixing or descending interface Input enclosure leakage characteristics Calculate the hold time 11 of 12

12 Actions Hold Time Pass Calculated hold time exceeds required hold time no remedial action required Remove fan and fan screen Remove test signage Re-instate test specific enclosure changes made. Provide test report Record date of test Actions Hold Time Fail Locate major leak paths