Room Integrity Testing using Door Fans & Alternative Technologies
Clean Agent fire suppression systems are used in enclosures where a sprinkler system would cause damage to sensitive contents such as computer servers, paper files or historical artifacts. Upon fire detection the compressed Clean Agent, which can be a halocarbon or an inert gas, is released into the enclosure as extinguishant. It is necessary to perform room integrity tests because they allow for the determination of both the Hold-Time and the Peak Pressure. This report will highlight the regulations and current testing methods. Finally, we will propose future and immediate integrity testing applications using the Portascanner™ Watertight Integrity Test Indicator for consideration. This unit is widely deployed in commercial Shipping, Naval vessels, Submarines and Offshore Oil & Gas Platforms. We will also attempt to anticipate some challenges.
Relation between Regulation and Testing
Even though the NFPA 2001 and the ISO 14520 standards set the requirements for many areas such as agent concentration for a number of areas of use, this report will only consider the recommendations and requirements set for enclosure design and testing. As inert and halocarbon agents function on the flooding principle, it is necessary to retain the agent within the enclosure for a critical amount of time in order for it to function. The total flooding principal involves the discharge of agent within the enclosure, until a minimum agent concentration is achieved. The realization of the minimum agent concentration is necessary to extinguish the fire. Therefore, it is imperative to maintain a certain enclosure integrity. However, it has been shown that the industry had previously put too much value on fully isolating the enclosure to retain the agent, as this had as stated an “adverse effect on the Peak Pressures created during the clean agent discharge, which can cause extensive damage to the enclosure itself.” 15 years of research conducted by major manufacturers in this area (Fike, 3M, Ansul, Kidde Fenwal, Chemetron and Retrotec) revealed that there was a relationship between the Peak Pressure and the Hold Time, and thus the models given by NFPA 2001 and ISO 14520 were under-predicting peak pressure. These results were published in the Pressure Relief Vent Area Guide under the FSSA (Fire Suppression Systems Association). Retrotec Energy, 2016.
In “Development and Validation of a Modified Clean Agent Draining Model for Total Flooding Fire Suppression Systems”, a thesis by Todd M. Hetrick released in 2009, it has been shown that models by the NFPA 2001 and ISO 14520 were inadequate for predicting the hold time. NFPA 2001 was based on a “sharp descending interface model”, describing the sharp change between air and the discharged agent, where no mixing occurs. This model was shown to over-predict the Hold Time, whereas the “wide descending interface”, as predicted by ISO 14520 describes an instantaneous mixing interface after discharge of agent, and this was conservatively predicting the Hold Time. The model suggested, namely the “thick descending interface model”, assumes an interface between air and discharged agent that is between the two previously stated extremes. (Hetrick, 2009).
Changes to Regulation
These discoveries have had major impacts on NFPA 2001 and ISO 14520, on the way enclosure integrity is tested and on the prediction models for Peak Pressure and Hold Time. Firstly, due to the discovery of the relationship between Peak Pressure and Hold Time, which can be perceived as “enclosure tightness”, NFPA 2001 has required Peak Pressure evaluations since 2008. ISO 14520 has always required Peak Pressure evaluations. Since the 2012 edition, NFPA 2001 requires a “specified enclosure pressure limit”2, which then also results in a “minimum allowable leakage area”3. (Genge, 2012). This thesis has also led to changes in the model used to predict Hold Times. Both NFPA 2001 and ISO 14520 now rely on prediction equations such as the FSSA equations, which are based on the new, more accurate model. Both standards now require two leakage area measurements of the enclosure during integrity testing, one is used to predict the Hold Time and the other is used to predict the maximum positive and negative Peak Pressure during discharge. Both standards recommend using Door Fan Testing to analysis the enclosure and retrieve the necessary values.
These changes and requirements can be paraphrased into the following two requirements as described by Fire Stop Company :
• “Make the room tight enough to have sufficient retention time according to NFPA or ISO.
• Make the room loose enough or provide vents to prevent enclosure damage at discharge.”
Current Testing Procedure
A Room Integrity Fan Test is performed to assure the protected room will hold the clean agent for the required period of time. It is a way to measure the leakage of an enclosure. A large fan is temporarily installed in the doorway of the room to be tested, with the fan blowing into the room (pressurizing the room). The fan speed is adjusted to obtain flow pressure equivalent to the pressure exerted during a fire suppression system discharge. The fan is then reversed on the door to draw air from the room (de-pressurizing the room). The airflow and pressure readings obtained are entered into a computer program designed to calculate the Equivalent Leakage Area (ELA) for the room. When a room has a suspended (drop) ceiling, then the Below Ceiling Leakage Area (BCLA) is calculated as one-half the total ELA and used in the calculations for Retention Time.
Given that most gaseous chemical agents used for fire suppression are heavier than air, the agent will begin to leak out of any lower level penetrations left unsealed. The rate at which the agent leaks is directly proportional to the amount of leakage at higher elevations of the room. As agent leaks out, fresh air replaces it from above. The point where fresh air above meets the concentration air mixture is called the Descending Interface.
Because of its nature, a Door Fan Test will always calculate the “worst case leakage” for the room. It draws air through leaks in the room and under the floor as well as above the suspended ceiling to predict the descending interface of the suppression agent. The length of time it takes for the Descending Interface to reach the minimum protected height identifies the concentration hold time.
The Portascanner™ II Watertight Integrity Test Indicator is a small hand-held ultrasonic unit featuring dual Decibel & Linear readings in the display and widely used in Shipping, Naval vessels, Submarines and Offshore Oil & Gas Platforms. The unit is the most mathematically accurate in the world, detecting leak apertures as small as 0.06mm with a tolerance of +/-0.02mm. It is lightweight, intuitive to use and supported by regional Service Stations in USA, UK, Dubai, India and Singapore. Carrying clips are added so that operators can operate hands-free.
There are several challenges that arise from using Portascanner™ as the device for testing enclosure integrity. The first being the identification of the leakage area value. The fan determines this by analyzing pressure differentials and using compressible flow through an aperture. Portascanner™ is ideal for determining the exact leakage location, thus it has the ability to determine if the enclosure is able to provide the necessary hold time. Nevertheless, it is also important to determine the exact leakage area value, so as to provide enough leakage to prevent pressure limits exceeding peak pressures. This also needs to be done for the enclosure as an entirety and not just a single leakage site. The challenge hereby would be to correlate the signal strength of the ultrasonic signal to a leakage area value. This would need to be tested in an experimental environment.
In addition to this, enclosure design needs to be considered. Receivers would need to be placed either on the outside of the enclosure or within the enclosure. The Generators would need to be placed accordingly. This needs to be addressed, as otherwise there might be leaks that go unnoticed if they are located in inaccessible places such as upper elevated areas of the enclosure. The Fan Door Test kit is capable of measuring total leakage area of the enclosure as an entirety from within the room (i.e. at the exit).
Fan Door testing has been in use for many years and is established as a very efficient and effective way to test for enclosure integrity and also makes it possible to predict Hold Times and Peak Pressures as requested by standards such as NFPA 2001 and ISO 14520.
Future Portascanner™ Application Proposal
We propose a model in which Portascanner™ can be used as an alternative the Door Fan Testing kit. In this model the Generator is placed in the enclosure. The ultrasonic signals, emitted by the three piezoelectric transducers, then travel throughout the enclosure and pass through any leakage sites. The Receiver, which is tuned to receive the specific frequency of the signal, is then placed outside the space to determine leakage sites.
However, to meet the requirements set by NFPA 2001 and ISO 14520, it is necessary to determine two values of leakage area, so that the Hold Time and the maximum positive and negative Peak Pressure can be determined. This is imperative to prevent both too much leakage of agent, which diminishes the functionality of the total flooding principle, and not enough leakage, which results in enclosure strength exceeding Peak Pressures. Both these effects would be severe in the event of fire.
Portascanner™ is able to provide the exact information about the location of leakage sites, with an accuracy of 0.06 mm and a tolerance of ±0.02 mm, and the interpretation of the seal i.e. watertight, weather tight or full leakage site. If it were possible to correlate the signal strength of the received signal by the Portascanner™ to the total leakage area and hence leak to volume ratio of the enclosure, then the “Future Portascanner(TM) “ model proposed would be able to replace Door Fan Testing in terms of integrity testing, by using the FSSA equations. (RetrotecEnergy, 2016).
Ideally, this would be conducted at all possible leakage sites, with an array of Receivers outside of the space. The leakage areas at all these points could then be combined into one hypothetical leakage site. This hypothesis is however, opposed by many challenges.