While the design of gaseous extinguishing systems is well catered for by systems standards, the issue of pressure venting when these systems are discharged has been overlooked – until now. Paul Coxon of AFP Air Technologies unveils the results of some groundbreaking tests.
Fixed gaseous systems are widely used in a variety of applications to protect property and assets from fire. On activation, these systems discharge agent into a space through a nozzles or nozzles, to flood its entire volume with gas. But the flooding of these spaces with gas can generate potentially high levels of pressure within a room – both positive and negative – so appropriate pressure relief venting is necessary for the safe operation of these systems.
Although there are British and international standards for the design and installation of gas systems, there are no formal standards for the design and operation of pressure relief venting.
Correct pressure venting is important because it can prevent structural damage to a room in the event of a discharge. Conversely, if a room has too much leakage, the system may fail to maintain the appropriate concentrations of gas, so compromising the ability of a system to extinguish a fire. It’s also important, therefore, that protected areas are tested for ‘room integrity’. By doing this, the leakage area in a room and therefore the time an appropriate concentration of the gas will be maintained before the agent leaks into the atmosphere, can be ascertained.
A better understanding of the performance of a pressure vent can be had if it can be fully calibrated – that is, tested in the fully open position with a standard room integrity test kit. This allows for any claims about the free vent areas and vent opening pressures to be assessed.
AFP Air Technologies has been developing pressure vents for many years to provide a high level of performance, exclusively for gas fire extinguishing systems. As there are no standards against which to approve our products, we developed a vent that could be tested in a live system using Retrotec’s integrity test fan kit. We needed to find out:
– whether the Retrotec kit could test the opening pressure of the vents?
– could the test kit provide enough pressure to fully open the vents?
– whether we could obtain information on the operation of the vents during live gas discharges?
With all this in mind, AFP Air Technologies undertook a series of tests, some of which were witnessed by BRE, to demonstrate the performance of their products and to progress the understanding of gas system pressure venting. We were supported in the tests by LPG Fire UK who provided IG55 and FM200 for the tests. Each system was designed by them using VDS Software.
Test facility
This comprised an ISO steel container with a wooden partition across the width, providing a test room with a volume of 43m3 with continuous measurement and recording of pressure, temperature, air flow and the degree of pressure vent blade opening. The tests and pressure vent blade operation were recorded on video.
A number of room integrity tests were conducted in accordance with the door fan test in BS ISO 14520 Annex E by an independent party. The three different vents used for the tests were:
– AFP’s HXD300 vent, 300 x 300mm opening and three vent blades
– AFP’s SHX300 vent, 300 x 300mm opening and three balanced weighted vent blades
– Another third party vent, 300 x 300mm opening and four ‘top hinged bottom weighted’ vent blades.
We also carried out a test on a 300 x 300mm square hole to determine the pressure of the risk as a bench mark, and to verify the VdS calculated risk pressure.
All three products added to the leakage area of the room, and so resulted in decreased gas retention times. But the leakage through the vents was considered acceptable and did not significantly compromise the integrity of the room. Both the HXD and SHX vents demonstrated effective opening and provided free vent areas approaching the maximum possible at pressures under 300 Pascals. The third party vent needed a significant pressure to initiate blade opening (around 170 Pascals) and the free vent area – even at 429 Pascals – was only 9% of the maximum of the product.
It was possible to fully calibrate the SHX vent (fully open at 95.5 Pascals) using the integrity test equipment. This feature in a pressure vent provides additional data on the product’s ability to appropriately mitigate room pressure, in the event of a gas discharge.
Gas discharge tests
A series of eight gas discharge tests were conducted, seven with a single IG-55 container, nominally pressurised to 300 bar, and one with HFC-227ea agent, nominally pressurised at 42 bar.
The HXD and SHX vents demonstrated effective pressure relief in the room on discharge of the IG-55 and reduced pressure to below 500 Pascals – in fact the peak room pressure with the SHX vent was comparable to that of an open hole. The HXD vent (acting as an under-pressure relief device with one blade taped close) provided effective pressure relief on discharge of the HFC-227ea chemical agent, whereas at 790 Pascals, the third party vent did not demonstrate effective pressure relief.
Tests 5 and 6 demonstrated that cascade venting into limited volumes needs to be considered. Significant pressures were generated by closing the doors of the ISO container; it was observed that the back-pressure generated in the outside the room of discharge caused the vents to open and close in an unpredictable manner.
Conclusions
Pressure venting in gas extinguishing systems is not specified widely enough and needs to be developed, as it is critical to the safe operation of gas systems. Venting is an issue for both inert and chemical agents. There are benefits in having vents that can be fully calibrated during room integrity testing. Test data on pressure vent operation is desirable and necessary as a basis of a formal specification.
Thanks to the tests witnessed by BRE, we have scientific evidence that the performance of our High-X pressure vents are well within the VdS parameters for a calculated free vent area, as neither of the units created a back pressure of more than 350 Pascals. The tests carried out on FM200 were helpful as the results show that with a positive pressure of over 1000 Pascals, FM200 and other chemical agents should be treated like inert gases with the risk sealed and the correct sized pressure vents fitted for negative pressure as well as positive pressure.
Following these tests and as a result of the data verified, a European standard or at least guidance from LPCB, VDS or other appropriate body needs to be formulated to provide a basis for third party verification that all pressure vents sold on the market meet certain levels of performance. We believe that the testing we undertook, and the verification carried out by BRE, sets the benchmark for pressure vent products and can easily be formulated into a testing standard for all to be approved to.
It is not as simple as using a fan to open the pressure vent at certain pressures, as this will not determine the risk of back pressure that can be produced. Only live discharge testing can achieve a true result.
In order to more fully understand the design and operation of pressure vents, we would propose testing in an actual fire scenario, where the pressures on discharge of an agent would be significantly increased. The implications of
cascade venting need to be addressed, and further investigation of backpressure could be considered.
Nevertheless, the tests have provided valuable new data on pressure venting for gas systems and we are communicating the results of the study to the wider fire safety community. It also intended to present the work to the ISO TC21/SC8 committee for consideration and possible development.
Acknowledgements
The author would like to thank Dr Tim Nichols of LPG and Colin Uzell of Retrotec for their assistance in conducting the tests.
While the design of gaseous extinguishing systems is well catered for by systems standards, the issue of pressure venting when these systems are discharged has been overlooked – until now. Paul Coxon of AFP Air Technologies unveils the results of some groundbreaking tests.
Fixed gaseous systems are widely used in a variety of applications to protect property and assets from fire. On activation, these systems discharge agent into a space through a nozzles or nozzles, to flood its entire volume with gas. But the flooding of these spaces with gas can generate potentially high levels of pressure within a room – both positive and negative – so appropriate pressure relief venting is necessary for the safe operation of these systems.
Although there are British and international standards for the design and installation of gas systems, there are no formal standards for the design and operation of pressure relief venting.
Correct pressure venting is important because it can prevent structural damage to a room in the event of a discharge. Conversely, if a room has too much leakage, the system may fail to maintain the appropriate concentrations of gas, so compromising the ability of a system to extinguish a fire. It’s also important, therefore, that protected areas are tested for ‘room integrity’. By doing this, the leakage area in a room and therefore the time an appropriate concentration of the gas will be maintained before the agent leaks into the atmosphere, can be ascertained.
A better understanding of the performance of a pressure vent can be had if it can be fully calibrated – that is, tested in the fully open position with a standard room integrity test kit. This allows for any claims about the free vent areas and vent opening pressures to be assessed.
AFP Air Technologies has been developing pressure vents for many years to provide a high level of performance, exclusively for gas fire extinguishing systems. As there are no standards against which to approve our products, we developed a vent that could be tested in a live system using Retrotec’s integrity test fan kit. We needed to find out:
• whether the Retrotec kit could test the opening pressure of the vents?
• could the test kit provide enough pressure to fully open the vents?
• whether we could obtain information on the operation of the vents during live gas discharges?
With all this in mind, AFP Air Technologies undertook a series of tests, some of which were witnessed by BRE, to demonstrate the performance of their products and to progress the understanding of gas system pressure venting. We were supported in the tests by LPG Fire UK who provided IG55 and FM200 for the tests. Each system was designed by them using VDS Software.
Test facility
This comprised an ISO steel container with a wooden partition across the width, providing a test room with a volume of 43m3 with continuous measurement and recording of pressure, temperature, air flow and the degree of pressure vent blade opening. The tests and pressure vent blade operation were recorded on video.
A number of room integrity tests were conducted in accordance with the door fan test in BS ISO 14520 Annex E by an independent party. The three different vents used for the tests were:
• AFP’s HXD300 vent, 300 x 300mm opening and three vent blades
• AFP’s SHX300 vent, 300 x 300mm opening and three balanced weighted vent blades
• Another third party vent, 300 x 300mm opening and four ‘top hinged bottom weighted’ vent blades.
We also carried out a test on a 300 x 300mm square hole to determine the pressure of the risk as a bench mark, and to verify the VdS calculated risk pressure.
All three products added to the leakage area of the room, and so resulted in decreased gas retention times. But the leakage through the vents was considered acceptable and did not significantly compromise the integrity of the room. Both the HXD and SHX vents demonstrated effective opening and provided free vent areas approaching the maximum possible at pressures under 300 Pascals. The third party vent needed a significant pressure to initiate blade opening (around 170 Pascals) and the free vent area – even at 429 Pascals – was only 9% of the maximum of the product.
It was possible to fully calibrate the SHX vent (fully open at 95.5 Pascals) using the integrity test equipment. This feature in a pressure vent provides additional data on the product’s ability to appropriately mitigate room pressure, in the event of a gas discharge.
Gas discharge tests
A series of eight gas discharge tests were conducted, seven with a single IG-55 container, nominally pressurised to 300 bar, and one with HFC-227ea agent, nominally pressurised at 42 bar.
The HXD and SHX vents demonstrated effective pressure relief in the room on discharge of the IG-55 and reduced pressure to below 500 Pascals – in fact the peak room pressure with the SHX vent was comparable to that of an open hole. The HXD vent (acting as an under-pressure relief device with one blade taped close) provided effective pressure relief on discharge of the HFC-227ea chemical agent, whereas at 790 Pascals, the third party vent did not demonstrate effective pressure relief.
Tests 5 and 6 demonstrated that cascade venting into limited volumes needs to be considered. Significant pressures were generated by closing the doors of the ISO container; it was observed that the back-pressure generated in the outside the room of discharge caused the vents to open and close in an unpredictable manner.
Conclusions
Pressure venting in gas extinguishing systems is not specified widely enough and needs to be developed, as it is critical to the safe operation of gas systems. Venting is an issue for both inert and chemical agents. There are benefits in having vents that can be fully calibrated during room integrity testing. Test data on pressure vent operation is desirable and necessary as a basis of a formal specification.
Thanks to the tests witnessed by BRE, we have scientific evidence that the performance of our High-X pressure vents are well within the VdS parameters for a calculated free vent area, as neither of the units created a back pressure of more than 350 Pascals. The tests carried out on FM200 were helpful as the results show that with a positive pressure of over 1000 Pascals, FM200 and other chemical agents should be treated like inert gases with the risk sealed and the correct sized pressure vents fitted for negative pressure as well as positive pressure.
Following these tests and as a result of the data verified, a European standard or at least guidance from LPCB, VDS or other appropriate body needs to be formulated to provide a basis for third party verification that all pressure vents sold on the market meet certain levels of performance. We believe that the testing we undertook, and the verification carried out by BRE, sets the benchmark for pressure vent products and can easily be formulated into a testing standard for all to be approved to.
It is not as simple as using a fan to open the pressure vent at certain pressures, as this will not determine the risk of back pressure that can be produced. Only live discharge testing can achieve a true result.
In order to more fully understand the design and operation of pressure vents, we would propose testing in an actual fire scenario, where the pressures on discharge of an agent would be significantly increased. The implications of
cascade venting need to be addressed, and further investigation of backpressure could be considered.
Nevertheless, the tests have provided valuable new data on pressure venting for gas systems and we are communicating the results of the study to the wider fire safety community. It also intended to present the work to the ISO TC21/SC8 committee for consideration and possible development.
Acknowledgements
The author would like to thank Dr Tim Nichols of LPG and Colin Uzell of Retrotec for their assistance in conducting the tests.
