m/V is the agent mass requirements (in kilogram per cubic metre); i.e. mass, m, in kilograms of agent required per cubic metre of protected volume V to produce the indicated concentration at the temperature specified.
V is the net volume of hazard (in cubic metre); i.e. the enclosed volume minus the fixed structures impervious to extinguishant.
Uoo-cjs
T is the temperature (in degree Celsius); i.e. the design temperature in the hazard area.
S is the specific volume (in cubic metre per kilogram); the specific volume of superheated HFC 125 vapour at a pressure of 1,013 bar may
be approximated by the formula:
S = k, + k2T
where i-| = 0,1825; A2= 0,0007.
c is the concentration (in percent); i.e. the volumetric concentration of HFC 125 in air at the temperature indicated, and a pressure of 1,013 bar.
Table 4 — HFC 125 reference extinguishing and design concentrations
|
Fuel |
Extinguishment % by volume |
Minimum design % by volume |
|
Class В Heptane (cup burner) Heptane (room test) |
9,3 9,3 |
12,1 |
|
Surface Class A Wood crib PM MA PP ABS |
6,7 8,6 8,6 8,6 |
11,2 |
|
Higher Hazard Class A |
a |
11,5 |
|
The extinguishment values for the Class В and the Surface Class A fuels are determined by testing in accordance with EN 15004-1:2008, Annexes В and C. The minimum design concentration for the Class В fuel is the higher value of the heptane cup burner or room test heptane extinguishment concentration multiplied by 1,3. The minimum design concentration for Surface Class A fuel is the highest value of the wood crib, PMMA, PP or ABS extinguishment concentrations multiplied by 1,3. In the absence of any of the 4 extinguishment values, the minimum design concentration for Surface Class A shall be that of Higher Hazard Class A. See EN 15004-1:2008, 7.5.1.3, for guidance on Class A fuels. The extinguishing and design concentrations for room-scale test fires are for informational purposes only. Lower and higher extinguishing concentrations than those shown for room-scale test fires may be achieved and allowed when validated by test reports from internationally recognized laboratories. |
||
a The minimum design concentration for Higher Hazard Class A fuels shall be the higher of the Surface Class A or 95 % of the Class В minimum design concentration.
Safety of personnel
Any hazard to personnel created by the discharge of HFC 125 shall be considered in the design of the system.
Potential hazards can arise from the following:
the extinguishant itself;
the combustion products of the fire;
breakdown products of the extinguishant resulting from exposure to fire.
For minimum safety requirements, see EN 15004-1:2008, Clause 5.
Toxicological information for HFC 125 is given in Table 5.
Table 5 — Toxicological information for HFC 125
|
Property |
Value % by volume |
|
ALCa |
>70 |
|
No observed adverse effect level (NOAEL) |
7,5 |
|
Lowest observed adverse effect level (LOAEL) |
10 |
|
a ALC is the concentration lethal for a rat population during a 4 h exposure. |
|
System design
Fill density
The fill density of the container shall not exceed the values given in Tables 6 and 7 for 25 bar and 42 bar systems, respectively.
Exceeding the maximum fill density may result in the container becoming “liquid full”, with the effect that an extremely high rise in pressure occurs with small increases in temperature, which could adversely affect the integrity of the container assembly.
The relationships between pressure and temperature are shown in Figures 1 and 2 for maximum fill density.
Table 6 — Storage container characteristics for HFC 125-25 bar
|
Property |
Unit |
Value |
|
Maximum fill density |
kg/m3 |
929 |
|
Maximum container working pressure at 50 °С |
bara |
40 |
|
Superpressurization at 20 °С |
bara |
25 |
|
Reference should be made to Figure 1 for further data on pressure/temperature relationships. |
||
|
a 1 bar = 0,1 MPa = 105 Pa; 1 MPa = 1 N/mm2. |
||
Table 7 — Storage container characteristics for HFC 125-42 bar
|
Property |
Unit |
Value |
|
Maximum fill density |
kg/m3 |
929 |
|
Maximum container working pressure at 50 °С |
bara |
63 |
|
Superpressurization at 20 °С |
bara |
42 |
|
Reference should be made to Figure 2 for further data on pressure/temperature relationships. |
||
|
a 1 bar = 0,1 MPa = 105 Pa; 1 MPa = 1 N/mm2. |
||
Superpressurization
Containers shall be superpressurized with nitrogen with a moisture content of not more than 60 x 10“4 % by mass to an equilibrium pressure of (25 + 1q25) bar and (42 + q’1) bar at a temperature of 22 °С (see Clause 1 for exception).
Extinguishant quantity
The quantity of extinguishant shall be the minimum required to achieve the design concentration within the hazard volume at the minimum expected temperature, determined using Table 3 and the method according to EN 15004-1:2008, 7.6.
The design concentrations shall be those specified for relevant hazards in Table 4, including a 1,3 safety factor on the extinguishing concentration. Consideration should be given to increasing this for particular hazards, while seeking advice from the relevant authority.
Y pressure, bar
Key
X temperature, °С
— Temperature/pressure graph for HFC 125 - Superpressurized with nitrogen
to 25 bar at 22 °С
Key
X temperature, °С
Y pressure, bar
— Temperature/pressure graph for HFC 125 - Superpressurized with nitrogen
to 42 bar at 22 °С
