Appendix 1: Analytical methods for determining Halon 1301 concentration levels

• ED Decision 2007/020/R found in: CS-25 Amdt 27 - Large Aeroplanes (Jan 2023)

Appendix 1: Analytical methods for determining Halon 1301 concentration levels ED Decision 2007/020/R 1. PURPOSE. This appendix contains analytical methods for determining Halon 1301 fire extinguishing agent concentration levels in empty or loaded cargo compartments as a function of time. 2. EXPLANATION OF TERMS AND SYMBOLS. TABLE 2-1. TERMS AND SYMBOLS <table border="1" cellpadding="0" cellspacing="0" width="606"><tr><td valign="top" width="89"><p><b>SYMBOL</b></p></td><td valign="top" width="286"><p><b>DESCRIPTION</b></p></td><td valign="top" width="231"><p><b>UNITS CONSISTENT WITH EQUATIONS</b></p></td></tr><tr><td valign="top" width="89"><p>C(t)</p></td><td valign="top" width="286"><p>Halon 1301 concentration by volume at time “t.”</p><p>= V_{Halon 1301} / V</p></td><td valign="top" width="231"><p>Dimensionless</p></td></tr><tr><td valign="top" width="89"><p>V_{Halon 1301}</p></td><td valign="top" width="286"><p>Volume of Halon 1301 in cargo compartment.</p></td><td valign="top" width="231"><p>Cubic metre - m³</p><p>(Cubic feet - ft³)</p></td></tr><tr><td valign="top" width="89"><p>V</p></td><td valign="top" width="286"><p>Cargo compartment free volume (i.e., volume not occupied by cargo).</p><p>= 1 - ( V_cargo / V_empty )</p></td><td valign="top" width="231"><p>Cubic metre - m³</p><p>(Cubic feet - ft³)</p></td></tr><tr><td valign="top" width="89"><p>V_cargo</p></td><td valign="top" width="286"><p>Cargo volume.</p></td><td valign="top" width="231"><p>Cubic metre - m³</p><p>(Cubic feet - ft³)</p></td></tr><tr><td valign="top" width="89"><p>V_empty</p></td><td valign="top" width="286"><p>Empty cargo compartment volume.</p></td><td valign="top" width="231"><p>Cubic metre - m³</p><p>(Cubic feet - ft³)</p></td></tr><tr><td valign="top" width="89"><p>T</p></td><td valign="top" width="286"><p>Time.</p></td><td valign="top" width="231"><p>Minutes – Min</p></td></tr><tr><td valign="top" width="89"><p>E</p></td><td valign="top" width="286"><p>Cargo compartment leakage rate.</p></td><td valign="top" width="231"><p>Cubic metre per minute - m³/min</p><p>(Cubic feet per minute - ft³/min)</p></td></tr><tr><td valign="top" width="89"><p>S</p></td><td valign="top" width="286"><p>Specific volume of Halon 1301.</p></td><td valign="top" width="231"><p>Cubic metre per kilogram m³/kg</p><p>(cubic feet per pounds(mass) ft³/lbm)</p></td></tr><tr><td valign="top" width="89"><p>R</p></td><td valign="top" width="286"><p>Halon 1301 flow rate.</p></td><td valign="top" width="231"><p>Kilogram per minute kg/min (pounds(mass) per minute lbm/min)</p></td></tr></table> 3. HALON 1301 CONCENTRATION LEVEL MODEL. Cargo compartment fire extinguishing systems generally use a combination of one or two types of Halon 1301 discharge methods. One type rapidly releases all of the fire extinguishing agent from one or more pressurised bottles into the cargo compartment. This type of discharge method is commonly known as a high rate discharge or ‘dump’ system. FIGURE 3-1. EXAMPLE - HALON 1301 MODEL ****** The second type of Halon 1301 discharge method slowly releases the fire extinguishing agent from one or more pressurised bottles into the cargo compartment. This type of discharge method is commonly known as a metering system. The following list provides some examples, not all-inclusive, of different combinations of these Halon 1301 discharge methods. a. One high rate discharge. b. One high rate discharge followed by a second high rate discharge at a specified later time. c. One high rate discharge followed by a metered discharge at a specified later time. d. Simultaneous high rate and metered discharges. The Halon 1301 fire extinguishing system described in paragraph 3.c. above utilises both types of discharge methods and is illustrated in Figure 3-1. Prior to Phase I - Initial High Rate Discharge of Halon 1301 This portion of the extinguishing process illustrates the high rate discharge method of releasing all of the fire extinguishing agent from one or more pressurised bottles into the cargo compartment. Phase I - Exponential “Decay” of Halon 1301 The beginning of Phase I represents the initial concentration of Halon 1301 used to knock down a cargo fire. Since no more Halon 1301 is introduced into the cargo compartment during Phase I, the concentration of Halon 1301 undergoes an exponential “decay” versus time. The governing equation for exponential “decay” during Phase I is the following: C(t) = C(0) e -E t /V NOTE - C(0) is the initial concentration of Halon 1301 used to knock down a cargo fire at the beginning of Phase I and t is the time elapsed since the beginning of Phase I. Phase II - Metered Discharge of Halon 1301 The metered discharge of Halon 1301 starts at the beginning of Phase II. The example in Figure 3-1 shows that the metering rate is set to release Halon 1301 into the cargo compartment at a rate which is slightly greater than the rate Halon 1301 is lost through cargo compartment leakage. The governing equation for metering during Phase II is the following: C(t) = [ C(0) - { R S / E } ] e -E t / V + { R S / E } NOTE - C(0) is the concentration of Halon 1301 at the end of Phase I and t is the time elapsed since the end of Phase I. Phase III - Exponential “Decay” of Halon 1301 The beginning of Phase III marks the end of Halon 1301 metering. As in Phase I, since no more Halon 1301 is introduced into the cargo compartment, the concentration of Halon 1301 undergoes an exponential “decay” versus time. The governing equation for exponential “decay” during Phase III is the same as during Phase I with one exception; C(0) is the concentration of Halon 1301 at the end of Phase II and t is the time since the end of Phase II.” [Amdt 25/4]