---

In 2

(E.12)

A] = exp

- In Q_lm (in P_m, - In 2)

In 2

(E.13)

If the leakage opening area has been recorded under E.2.6.4 then, for subsequent calculations, should be multiplied by:

ELA + leakage opening area

ELA

where ELA is the measured ELA of the enclosure from E.2.7 using Equations (E.30) and (E.32) and leakage opening area is determined according to E.2.6.4.

E.2.8.6 Correlation and simplifying constants

Calculate the correlation constant k₂ using the equation:

k, = k —

¹ 4 2

(E.14)

Calculate the simplifying constant k₃ using the equation:

for extinguishants heavier than air (p_a< p_e)

F
1-F

(E.15)

for extinguishants lighter than air (p_a> p_e)

1-F Pmi + Pa ,.

I F

(E.16)

Calculate the simplifying constant k_A using the equations:

for extinguishants heavier than air (p_a< p_e)

_ 2P_hh

Л4 —

( F

Pmi + Pa

(E.17)

for extinguishants lighter than air (p_a> p_e)

p + p г mi гр

IP

bh

(1-F

(E.18)

E.2.8.7 Predicted hold time: standard enclosures without continuous mixing

For standard enclosures without continuous mixing, the predicted hold time, t, for the extinguishant concentration at height, H, to fall from the concentration q to <?_min may be calculated by assuming the extinguishant distribution in the enclosure, and calculating the hold time for an equivalent sharp interface

which would give the same column pressure and rate of loss of extinguishant as the actual extinguishant distribution.

In this calculation procedure it is assumed that:

1. the enclosure is a standard enclosure;

2. that for extinguishants heavier than air the extinguishant concentration at any particular instant equals the initial concentration (c.) from the lower boundary of the enclosure up to a certain height, and above this decreases linearly with increasing height to zero at the upper boundary of the enclosure; for extinguishants lighter than air the extinguishant concentration at any particular instant equals the initial concentration (Ci) from the upper boundary of the enclosure down to a certain height, and below this it decreases linearly with decreasing height to zero at the lower boundary of the enclosure.

Assume F = 0,5 and calculate the predicted hold time as follows: for extinguishants heavier than air (p_a < p_e)

V

(E.19)

(E.20)

Ґ{к₃Н_й+к^~^п-(к₃Н_е+к₄У

H_o I (1 - и) k₂F k₃

for extinguishants lighter than air (p_a> p_e)

k₃H₀+k₄rⁿ-(k₃(H₀-H_e)+k₄)^l-ⁿ

—n) k₂(ї —F) k₃

E.2.8.8 Predicted hold time: enclosures of any shape with continuous mixing

For enclosures of any shape with continuous mixing, assume F = 0,5 and calculate the predicted hold time, t, for the extinguishant concentration in the enclosure to fall from the initial concentration, a, to the concentration c_min (see 7.8) using the equation:

for extinguishants heavier than air (p_a< p_e)

F ^p"?

^l~~Fkl J

Pmf

2g_nH_o(p_m-p_a^ⁿ^2P_bh{p_m-p_ar”

^dP_m

(E.21)

P_m+ Pa

for extinguishants lighter than air (p_a > p^

( v”

^V

(E.22)

^P' 2g_nH₀(p_a-pJ^^₊2P_bh(p_a-pJ¹’'

(1-F)k₂ J A-fY⁷”

^P~ P_m+Pa—^

I < t J J

Solve the equation by a method of approximation, for example by using Simpson's Rule using an even number (not less than 20) of intervals.

E.2.8.9 Predicted hold time for non standard enclosures without continuous mixing

E.2.8.9.1 Determine the variation of horizontal cross-sectional area of the enclosure with height

.

E.2.8.9.2 In this calculation procedure it is assumed, for extinguishants heavier than air, the extinguishant concentration at any particular instant equals the initial concentration, c_if from the lower boundary of the enclosure up to a certain height, and above this decreases linearly with increasing height to zero at the upper boundary of the enclosure. For extinguishants lighter than air the extinguishant concentration at any particular instant equals the initial concentration (c,) from the upper boundary of the enclosure down to a certain height, and below this it decrease linearly with decreasing height to zero at the lower boundary of the enclosure.

E.2.8.9.3 Assume F= 0,5 and solve the following equation by analytical or numerical method to calculate the predicted hold time, t:

100 fl
r = — dV_e

Ci J Q ^e

(E.23)

With the aid of the following substitutions:

(E.24)

(E.25)

NOTE ‘d depends upon 'Л’; ‘с' depends upon ‘h’ and the interface height.

P_m=gn p_e~Pa

0

For extinguishants heavier than air (p_a < p_e)

/ Y

^{Q = Fk}^ - ^2Рт+₍^2Р"_Т

Pmi + Pa I 77 I

I )

(E.26)

(E.27)

For extinguishants lighter than air (p_a > p_e)

2Р_т+2Рьь

acdh

dl' =

100

acdh

100

(E.28)

Pm, + Pa

An approximate value of the hold time may be found by making a simplifying assumption when solving Equation (E.23). This approximate value will be shorter than or equal to an accurate solution. To obtain the approximate value of hold time, assume P_m is fixed at its initial value (when c = c_t throughout the enclosure) and calculate the resulting value of Q. Inserting this fixed value of Q in equation (E.23) gives:

/ = 100

(V -V
^rei ^ref

(E.29)

E.3 Treatment of enclosures with predicted hold times less than the recommended value

E.3.1 General

If the predicted hold time, calculated in accordance with E.2, is less than as recommended in 7.8.2 c), then E.3.2 to E.3.4 may be implemented as necessary.

E.3.2 Leakage areas

To quantify the scale of the problem calculate the effective leakage area, A_e, from the equation:

/ ^l/2 / 41/2

A_e=Q_ref^- =k_lP_ref"-°⁵^- (E.30)

ref J ²J

At 20 °С and 1,013 bar, equation E.29 reduces to:

4=0,7762 ^ P_re/-°'⁵ (E.31)

The equivalent leakage area, ELA, may be calculated as:

^ELA=W, ^(E32)

The ELA is used for fan calibration checks and for identification of actual leaks. It is the area of a circular sharp edged orifice which has the same value of A_e as the actual leakage area at the reference pressure differential.

E.3.3 Improved sealing of the enclosure

Consideration should be given to improving the sealing of the enclosure. If the sealing is improved and the new predicted hold time, after new fan test measurements in accordance with E.2.7.4, is not less than the minimum recommended value, no further action is necessary.

E.3.4 Quantification and location of leaks

E.3.4.1 General

For extinguishants heavier than air, extinguishant/air mixture will escape through the lower leaks and air will flow in through the upper leaks; for extinguishants lighter than air, extinguishant/air mixture will escape through the upper leaks and air will flow in through the lower leaks. In an enclosure without bias pressure the ‘neutral plane’ (between inflow and outflow) can be taken as the mid height of the enclosure. For the purpose of this assessment, lower leaks are assumed to be those below the neutral plane, and upper leaks are those above it.

The fan test does not show the location of the leaks or the value of the lower leakage fraction F. In E.2.8.7 to E.2.8.9, it is assumed that the value of F is 0,5, all the lower leaks are in the base of the enclosure and all the upper leaks are in the top of the enclosure. This is the worst case and gives the minimum value for hold time.

If some lower leaks are above the base of the enclosure or if some upper leaks are below the top of the enclosure, the hold time will be under-estimated but a simple mathematical treatment of this case is not possible.

The hold time will also be under-estimated if F is not 0,5 and the effect of this can be calculated.

E.3.4.2 Second calculation of hold time

Make a second calculation of the hold time, t, assuming F = 0,15. If this value is more than the recommended minimum (see 7.8.2 c)) then make an estimate of the actual value of F using the method in E.3.4.3.

E.3.4.3 Method of estimating F

Temporarily seal upper leaks, such as dampers, that can be traced using smoke. Repeat the fan test and calculate the reduced equivalent leakage area ELA2 using Equations (E.30) to (E.32).

Unseal the upper leaks and temporarily seal lower leaks that can be traced using smoke. Repeat the fan test and calculate the reduced equivalent leakage area ELA3 using Equations (E.30) to (E.32).

The area of the temporarily sealed upper leaks and lower leaks can thus be quantified and the remaining open area treated as 50 % upper leaks and 50 % lower leaks. Calculate the new value of F using ELA1 as the original ELA measurement:

„ ELA, + ELA. - ELA.

^{F = 0}’⁵ (E.33)

E.3.4.4 Final calculation of hold time

Using the value of F determined as in E.3.4.3, recalculate the hold time, t. For extinguishants heavier than air, F should not be more than 0,5 or less than 0,15. If F is less than 0,15 use F = 0,15. If F is greater than 0,5 use F= 0,5. For extinguishants lighter than air, F should not be less than 0,5 or more than 0,85; if F is less than 0,5 use F = 0,5, if F is greater than 0,85 use F = 0,85.

Extreme values of F, close to 0 or 1, may yield unrealistically long predicted hold times. If the outlet leakage area (lower or upper, depending on whether the extinguishant is heavier or lighter than air) is large then air flow in, as well as the mixture flow out, may occur at the outlet — invalidating the hold time equations.

E.4 Report

Prepare a written report containing the following information:

1. enclosure leak flow characteristics (i.e. the average values of k-i, and n);

2. initial concentration of extinguishant, minimum concentration, and the extinguishant to be used;

3. quantity of extinguishant provided;

4. net volume of the enclosure;

5. height of the enclosure, and for a non standard enclosure the appropriate dimensions;

6. for an enclosure without continuous mixing, the required protected height;

7. predicted hold time and whether or not the value complies with the recommendation of 7.8.2 c), i.e. whether it is less than 10 min or the higher necessary value, as appropriate;

8. information on the arrangement and status of the enclosure, surroundings and services as specified in E.2.5 and E.2.7.1.4;

9. current calibration data for the fan unit and the pressure measuring devices, corresponding certificates if available, and the results of the field calibration check;

10. test results, including a record of the test measurements and any appropriate calculations;

11. size and location of leaks, if identified.Annex F

(informative)

System performance verification

A suitable procedure for verification of the system is as follows.

1. Every 3 months; test and service all electrical detection and alarm systems as recommended in the appropriate national standards.

2. Every 6 months: perform the following checks and inspections:

1. externally examine pipework to determine its condition; replace or pressure test and repair as necessary pipework showing corrosion or mechanical damage;

2. check all control valves for correct manual function and automatic valves additionally for correct automatic function;

3. externally examine containers for signs of damage or unauthorized modification, and for damage to system hoses;

4. check pressure gauges of extinguishing containers, liquefied gas should be within 10% and non­liquefied gases within 5 % of correct charge pressure; replace or refill any showing a greater loss;

5. for liquefied gases, check weigh or use a liquid level indicator to verify correct content of containers. Replace or refill any showing a loss of more than 5 %.

3. Every 12 months: carry out a check of enclosure integrity using the method described in 9.2.4.1. If the measured aggregate area of leakage has increased from that measured during installation which would adversely affect system performance, carry out work to reduce the leakage.

As required by statutory regulations, but otherwise when convenient, remove the containers and pressure test when necessary.Annex G

(informative)

Safe personnel exposure guidelines

G.1 General

This Annex contains information to establish the practices necessary to prevent the unnecessary exposure of personnel to agent discharges or post discharge atmospheres containing the agents covered by this document.

The safety precautions required by this document do not address toxicological or physiological effects associated with the products of combustion caused by fire. The maximum exposure time assumed by the safety precautions in this document is 5 min. Exposure times longer than 5 min may involve physiological or toxicological effects not addressed by this document. The requirements given in 5.2 and 5.3 of this document for the installation and use of time delay devices, automatic/manual switches and disable devices shall apply to this Annex.

G.2 Safety

Any agent that is to be recognized by this document or proposed for inclusion in this document shall first be evaluated in respect to environmental aspects by European or by other international/national extinguishing agent approval institution.

NOTE Evaluation can be carried out e.g. in a manner equivalent to the U.S. Environmental Protection Agency's (EPA) SNAP Programme.

G.3 Hazards to Personnel

G.3.1 Agent itself

The discharge of gaseous agent systems to extinguish a fire could create a hazard to personnel from the natural form of the agent itself or from the products of decomposition that result from exposure of the agent to the fire or hot surfaces. Unnecessary exposure of personnel, either to the natural agent or to the decomposition products, should be avoided.

G.3.2 Noise

Discharge of a system can cause noise loud enough to be startling but ordinarily insufficient to cause traumatic injury.

G.3.3 Turbulence

High-velocity discharge from nozzles could be sufficient to dislodge substantial objects directly in the path. System discharge can cause enough general turbulence in the enclosures to move unsecured paper and light objects.

G.3.4 Low temperature

Direct contact with liquefied extinguishants being discharged from a system will have a strong chilling effect on objects and can cause frostbite burns to the skin. The liquid phase vapourizes rapidly when mixed with air and thus limits the hazard to the immediate vicinity of the discharge point. In humid atmospheres, minor reduction in visibility can occur for a brief period due to the condensation of water vapour.

G.4 Halocarbon agents

G.4.1 Toxicity of halocarbons (liquefied gases)

G.4.1.1 Table G.1 provides information on the toxicological effects of halocarbon agents covered by this document. The NOAEL is the highest concentration at which no adverse physiological or toxicological effect has been observed. The LOAEL is the lowest concentration at which an adverse physiological or toxicological effect has been observed.

G.4.1.2 An appropriate protocol measures the effect in a stepwise manner such that the interval between the LOAEL and NOAEL is sufficiently small to be acceptable to the competent regulatory authority. The EPA includes in its SNAP evaluation this aspect (of the rigour) of the test protocol.

Table G.1 — Toxicity information for halocarbon clean agents

G.4.1.3 For halocarbons covered in this Annex, the NOAEL and LOAEL are based on the toxicological

effect known as cardiac sensitization. Cardiac sensitization occurs when a chemical causes an increased sensitivity of the heart to adrenaline, a naturally occurring substance produced by the body during times of stress, leading to the sudden onset of irregular heart beats and possibly heart attack. Cardiac sensitization is measured in dogs after they have been exposed to a halocarbon agent for 5 min. At the 5 min time period, an external dose of adrenaline (epinephrine) is administered and an effect is recorded, if the dog experiences cardiac sensitization. The cardiac sensitization potential as measured in dogs is a highly conservative indicator of the potential in humans. The conservative nature of the cardiac sensitization test stems from several factors, the two most pertinent are as follows: