Страница 11: ДСТУ EN 15004-1:2014. Fixed firefighting systems. Gas extinguishing systems. Design, installation and maintenance (61474)

1. very high doses of adrenaline are given to the dogs during the testing procedure (doses are more than 10 x higher than the highest levels secreted by humans under maximum stress);

2. 4 x to 10 x more halocarbon is required to cause cardiac sensitization in the absence of externally administered adrenaline, even in artificially created situations of stress or fright in the dog test.

G.4.1.4 Because the cardiac sensitization potential is measured in dogs, a means of providing human relevance to the concentration at which this cardiac sensitization occurs (LOAEL) has been established through the use of physiologically based pharmacokinetic (PBPK) modelling.

G.4.2 PBPK Model

G.4.2.1 A PBPK model is a computerized tool that describes time-related aspects of a chemical's distribution in a biological system. The PBPK model mathematically describes the uptake of the halocarbon into the body and the subsequent distribution of the halocarbon to the areas of the body where adverse effects can occur. For example, the model describes the breathing rate and uptake of the halocarbon from the exposure atmosphere into the lungs. From there, the model uses the blood flow bathing the lungs to describe the movement of the halocarbon from the lung space into the arterial blood that directly feeds the heart and vital organs of the body.

G.4.2.2 It is the ability of the model to describe the halocarbon concentration in human arterial blood that provides it primary utility in relating the dog cardiac sensitization test results to a human who is unintentionally exposed to the halocarbon. The concentration of halocarbon in the dog arterial blood at the time the cardiac sensitization event occurs (5 min exposure) is the critical arterial blood concentration, and this blood parameter is the link to the human system. Once this critical arterial blood concentration has been measured in dogs, the EPA-approved PBPK model simulates how long it will take the human arterial blood concentration to reach the critical arterial blood concentration (as determined in the dog test) during human inhalation of any particular concentration of the halocarbon agent. As long as the simulated human arterial concentration remains below the critical arterial blood concentration, the exposure is considered safe. Inhaled halocarbon concentrations that produce human arterial blood concentrations equal to or greater than the critical arterial blood concentration are considered unsafe because they represent inhaled concentrations that potentially yield arterial blood concentrations where cardiac sensitization events occur in the dog test. Using these critical arterial blood concentrations of halocarbons as the ceiling for allowable human arterial concentrations, any number of halocarbon exposure scenarios can be evaluated using this modelling approach.

G.4.2.3 In the dog cardiac sensitization test on Halon 1301, a measured dog arterial blood concentration of 25,7 mg/l is measured at the effect concentration (LOAEL) of 7,5 % after a 5 min exposure to Halon 1301 and an external intravenous adrenaline injection. The PBPK model predicts the time at which the human arterial blood concentration reaches 25,7 mg/l, for given inhaled Halon 1301 concentrations. Using this approach the model also predicts that at some inhaled halocarbon concentrations, the critical arterial blood concentration is never reached, and thus, cardiac sensitization will not occur. Accordingly, in the Tables G.2 to G.3, the time is arbitrarily truncated at 5 min, because the dogs were exposed for 5 min in the original cardiac sensitization testing protocols.

G.4.2.4 The time value, estimated by the EPA-approved and peer-reviewed PBPK model or its equivalent, is that required for the human arterial blood level for a given halocarbon to equal the arterial blood level of a dog exposed to the LOAEL for 5 min. For example, if a system is designed to achieve a maximum concentration of 12 % HFC-125, then personnel exposure can be no longer than 1,67 min. Examples of suitable exposure limiting mechanisms include seif-contained breathing apparatus and planned and rehearsed evacuation routes.

G.4.2.5 The requirements for pre-discharge alarms and time delays are intended to prevent human exposure to agents during fire fighting. However, in the unlikely circumstance that an accidental discharge occurs, restrictions on the use of certain halocarbon agents covered in this document are based on the availability of PBPK modelling information. For those halocarbon agents, in which modelling information is available, the exposure to those concentrations is limited to the times specified in the Tables G.2 to G.3 and under no circumstances should exceed 5 min. These concentrations and times are those that have been predicted to limit the human arterial blood concentration to below the critical arterial blood concentration associated with cardiac sensitization. For halocarbon agents, where the needed data are unavailable, the agents are restricted based on whether the protected space is normally occupied or unoccupied, and how quickly egress from the area can be effected. Normally occupied areas are those intended for human occupancy. Normally unoccupied areas are those in which personnel can be present from time to time. Therefore, a comparison of the cardiac sensitization values to the intended design concentration would determine the suitability of a halocarbon for use in normally occupied or unoccupied areas. [To keep oxygen concentrations above 16 5 (sea level equivalent), the point at which onset of impaired personnel function occurs, no halogenated fire extinguishing agents addressed in this document should be used at a concentration greater than 24 % in a normally occupied area.]

G.4.3 Safe exposure guidelines for halocarbons

G.4.3.1 Any unnecessary exposure to halocarbon clean agents, even at NOAEL concentrations, and halocarbon decomposition products shall be avoided. The requirements for pre-discharge alarms and time delays are intended to prevent human exposure to agents. The following additional provisions shall apply in order to account for failure of these safeguards.

G.4.3.2 Halocarbon systems for spaces that are normally occupied and designed to concentrations up to the NOAEL (see Table G.1) shall be permitted provided that the maximum exposure time does not exceed 5 min (i.e. escape of all occupants shall be achieved within 5 min).

G.4.3.3 Halocarbon systems for spaces that are normally occupied and designed to concentrations above the NOAEL and up to the LOAEL (see Table G.1 and EN 15004-2 to EN 15004-10), shall be permitted, given that exposure is limited to no longer than the time specified in Tables G.2 and G.3 corresponding to the given design concentration.

G.4.3.4 In spaces that are not normally occupied and protected by a halocarbon system designed to concentrations above the LOAEL (see Table G.1), and where personnel could possibly be exposed, exposure times are limited to those given in Tables G.2 and G.3.

G.4.3.5 In the absence of the information needed to fulfil the conditions listed in G.4.3.3 and G.4.3.4, the

following provisions shall apply for normally unoccupied areas:

1. where egress takes longer than 30 s but less than 1 min, the halocarbon agent shall not be used in a concentration exceeding its LOAEL;

2. concentrations exceeding the LOAEL are permitted only in areas not normally occupied by personnel provided that any personnel in the area can escape within 30 s; no unprotected personnel shall enter the area during agent discharge.

Table G.2 —Time for safe human exposure at stated concentrations for HFC-125

Table G.3 — Time for Safe Human Exposure at Stated Concentrations for HFC-227ea

G.5 Inert Gas (non-liquefied gas)

G.5.1 Physiological effects of inert gas agents

G.5.1.1 Table G.4 provides information on physiological effects of inert gas agents covered by this document. The health concern for inert gas clean agents is asphyxiation and hypoxic effects due to the lowered oxygen levels. With inert gas agents, an oxygen concentration of not less than 12% (sea level equivalent) is required for normally occupied areas. This corresponds to an agent concentration of not more than 43 %.

Table G.4 —Physiological effects for inert gas agents

G.5.1.2 IG-541 uses carbon dioxide to promote breathing characteristics intended to sustain life in the

oxygen-deficient environment for protection of personnel. Care should be taken not to design inert gas-type systems for normally occupied areas using design concentrations higher than that specified in the system manufacturer's listed design manual for the hazard being protected.

G.5.1.3 Inert gas agents do not decompose measurably in extinguishing a fire. As such, toxic or corrosive decomposition products are not found. However, heat and breakdown products of the fire itself can still be substantial and could make the area untenable for human occupancy.

G.5.2 Safe exposure guidelines for inert gas agents

G.5.2.1 Unnecessary exposure to inert gas agent systems resulting in low oxygen atmospheres shall be avoided. The requirements for pre-discharge alarms and time delays are intended to prevent human exposure to agents. The additional provisions given in G.5.2.2 to G.5.2.5 shall apply in order to account for failure of these safeguards.

G.5.2.2 Inert gas systems designed to concentrations below 43 % (corresponding to an oxygen concentration of 12 %, sea level equivalent of oxygen) shall be permitted, given the following:

1. the space is normally occupied;

2. means are provided to limit exposure to no longer than 5 min.

G.5.2.3 Inert gas systems designed to concentrations between 43 % and 52 % (corresponding to between 12 % and 10 % oxygen, sea level equivalent of oxygen) shall be permitted, given the following:

1. the space is normally occupied;

2. means are provided to limit exposure to no longer than 3 min.

G.5.2.4 Inert gas systems designed to concentrations between 52 % and 62 % (corresponding to between 10 % and 8 % oxygen, sea level equivalent of oxygen) shall be permitted given the following:

1. the space is normally unoccupied;

2. where personnel could possibly be exposed, means are provided to limit the exposure to less than 30 s.

G.5.2.5 Inert gas systems designed to concentrations above 62 % (corresponding to 8 % oxygen or below, sea level equivalent of oxygen), shall only be used in normally unoccupied areas where personnel are not exposed to such oxygen depletion. (See Clause 7, Table 5 for atmospheric correction factors.)Annex H

(informative)

Flow calculation implementation method and flow calculation verification
and testing for approvals

NOTE This Annex is taken from ISO 14520-1:2006 but has not been discussed in the responsible ISO/ТС 21/SC 8. Intensive discussion regarding this subject is necessary.

H.1 General

This Annex outlines recommended requirements for developing a flow calculation method of predicting critical flow parameters and an acceptable degree of accuracy.

H.2 Calculation method implementation

The following parameters should be considered in developing a flow calculation method (software):

1. percent of agent in pipe;

2. minimum distance from agent storage;

3. minimum and maximum discharge time;

4. minimum and maximum pipeline flow rates;

5. minimum and maximum agent velocities (in pipelines);

6. variance of piping volume to each nozzle;

7. maximum nozzle pressures variance (within a pipe arrangement);

8. nozzle pressure reducing orifices maximum and minimum area relative to inlet pipes area;

9. maximum imbalance agent arrival time and maximum imbalance agent run-out time between nozzles;

10. types of tee splits and related critical lengths;

11. tee orientation;

12. minimum and maximum flow split;

13. pipe and fitting types;

n) elevation changes;

15. system design temperature;

16. system operating temperatures.

H.3 Minimum accuracy recommendations

H.3.1 Physical quantities

1. System discharge time: ± 1 s, or ± 10 % of the discharge time if over 10 s (liquefied gases); ± 10 s over 60 s (non liquefied gases).

2. Average nozzle pressure ± 10 %.

3. Quantity of agent discharged from each (nozzle): ± 10 %.

Furthermore the standard deviation of the percentage differences between the measured and predicted agent quantities, relative to zero, should not exceed 5 %.

H.3.2 Recommended design limits to be included inside the flow calculation method (software)

The following design limits should be included inside the flow calculation method and verified by testing:

1. container volume, fill density, storage pressure;

2. nozzle area ratio (considering nozzle types and sizes);

3. nozzle pressure;

4. system discharge time;

5. tee split ratios (bull and side tees);

6. tee orientations;

7. critical piping distance around tees;

8. degree of imbalance between nozzles;

NOTE This can be expressed as nozzle liquid arrival and run-out time imbalances, by pipe volume imbalances or other methods used to control the imbalance in pipe layouts.

9. minimum and maximum agent velocities/flow rates;

10. system pipe volume;

11. pipe and fitting types and schedules;

12. system temperature.

H.4 Recommended testing procedure for system flow calculation method (software) validation

H.4.1 General

1. Five systems of 3 or 4 nozzles (these are the system manufacturer-submitted tests) should be designed (utilizing the flow calculation method that should be validated) constructed and discharge tested.

2. A report containing the test data results and the calculation predictions should be sent to the approval authority for examination.

3. Upon a positive examination of the pre-witness tests reports, the approval authority should proceed with testing.

4. Two of the system manufacturer submitted tests should be set up and discharge tested to confirm the test results already submitted to the approval authority.

5. The approval authority may ask for the design of at least three more tests that should include a specific set of design limits (in accordance with H.2) as stated by the manufacturers.

6. The tests will be designed, constructed and discharge tested with the approval authority present.

7. All these tests shall pass the requirements in accordance with H.5.

8. The system to be tested should be maintained and tested at a design temperature (usually 21 °С); however the test may be conducted at different temperatures with appropriate temperature correction calculations.

9. When the flow calculation software is capable of predicting calculation at temperatures other than the design reference temperature (usually 21 °С), verification tests should be conducted throughout the temperature range specified.

H.4.2 System design fortesting

The system to be tested should be designed at the limits of the flow calculation method (software) and should consider the hardware limitations.

The following flow calculation method design limits should be included inside the system piping layouts to be tested:

1. cylinder volume, fill density storage pressure;

2. nozzle area ratio (considering nozzle types and sizes);

3. nozzle pressure;

4. system discharge time;

5. tee split ratios (bull and side tees);

6. tee orientations;

7. critical piping distance around tees;

8. degree of imbalance between nozzles;

NOTE This can be expressed as nozzle liquid arrival and run-out time imbalances, by pipe volume imbalances, or other methods used to control the imbalance in pipe layouts.

9. minimum and maximum agent velocities/flow rates;

10. system pipe volume;

11. pipe and fitting types and schedules;

12. system temperature.

H.5 Pass/fail criteria

The system discharge time, the average nozzle pressure, and the quantity of agent delivered from each nozzle should be measured in the discharge tests.

These measurements should be compared to the predicted values from the software/methodology with the following pass/fail requirements:

• system discharge time;

• average nozzle pressure; ± 10 %;

• quantity of agent discharged ±10 %;

• furthermore the standard deviation of the percentage differences between the measured and predicted agent quantities, relative to zero should not exceed 5 %;

• design limits;

should be verified in accordance with H.3.1.Bibliography

1] ISO 5660-1, Reaction-to-fire tests - Heat release, smoke production and mass loss rate - Part 1: Heat release rate (cone calorimeter method)

'2] EN 13306, Maintenance terminology