Gaseous Fire Extinguishing Systems - HCFC-125 Extinguishing Systems

IS 15835 Key Formulas, Tables & Specifications - Scope

1. Pipe Sizing (Clause 12.3)

• Pipe sizing balances pressure loss and flow velocity in two-phase flow.
• Use Table 9 for pipe size vs flow rate (kg/s) based on pipe length:

• Verify with approved flow calculation software.

2. Enclosure Volumes (Clause 7.3.1)

• Net enclosure volume:

[ V_{Mn} = V - V_o ]

• Where:
  • (V) = gross enclosure volume (m³)
  • (V_o) = volume of permanent objects impermeable to gas (m³)
• Minimum net volume considers occupancy objects.

3. Design Concentration of HCFC-125 (Clause 8)

• Minimum design concentration:

• Adjust agent quantity for altitude using Table 8:

4. **Total Flooding Quantity (Clause

IS 15835 Key References:

1. Pipe Sizing (Clause 12.3, Table 9)

• Pipe diameter selection depends on flow rate and pipe length.
• Example from Table 9 (Flow rate in kg/s):

2. HCFC-125 Gas Specifications (Clause 4.5, Table 2)

• Purity ≥ 99%
• Moisture ≤ 0.001% by weight
• Acidity ≤ 3 ppm (HCl equivalent)
• Non-volatile residue ≤ 0.05 g/100 ml

3. Physical Properties of HCFC-125 (Clause 4.6, Table 3)

• Molecular mass: 120.02
• Boiling point: -48.5°C
• Vapour pressure at 20°C: 1.21 MPa
• Liquid density at 20°C: 1218 kg/m³

4. Design Concentration (Clause 8, Table 7 & 8)

• Minimum design concentration for Class A fires: 8% volume (6.6% extinguishing + 20% safety)
• For Class B fuels: 11.3% volume (8.6% + 30% safety)
• Atmospheric correction factor adjusts agent quantity for altitude (Table 8):

IS 15835: General Information Key Data for HCFC-125 Gas

1. HCFC-125 Gas Specifications (Table 2)

2. Physical Properties (Table 3)

3. Toxicological Data (Table 4 & 5)

• NOAEL: 7.5% volume (75,000 ppm)
• LOAEL: 10% volume (100,000 ppm)
• 4-hour Lethal Concentration (LC50): >70%
• Safe human exposure times vary inversely with concentration (e.g., 5 min at ~7.5–11.5%).

4. Pipe Sizing Guide (Table 9)

IS 15835: Key Gas Characteristics and Properties for HCFC-125

1. Chemical Composition (Clause 4.3, Table 1)

• Chemical formula: CHF₂CF₃
• Chemical name: Pentafluoroethane (99.85% purity)
• Commercial name: HCFC-125

2. Specification for HCFC-125 Gas (Clause 4.5, Table 2)

3. Physical Properties (Clause 4.6, Table 3)

4. Toxicological Data (Clause 4.7, Tables 4 & 5)

IS 15835 Key Points: Safety & Miscellaneous Hazards

1. Miscellaneous Hazards (Clause 5.2)

• Cold Temperatures: Direct contact with discharged HCFC-125 liquid causes frostbite; hazard limited near nozzle.
• Visibility: Discharge may cause mist but rarely affects visibility; HCFC-125 detectable above 3% concentration.
• Uneven Distribution: HCFC-125 vapors are denser than air, can accumulate in low areas; use well-designed nozzles for uniform mixing.

2. Design Concentration (Clause 8.6)

• Class B fuels (Heptane):
  [ \text{Design Conc.} = 8.6% \times 1.3 = 11.3% ]
• Class C (Electrical):
  [ \text{Design Conc.} = 6.6% \times 1.2 = 7.92% ]
• For mixed hazards, use highest required concentration.
• Safety factors: 20-30% depending on fuel type.

3. Atmospheric Correction Factor (Table 8)

Formula:

[ N_a = N \times \frac{P_{ambient}}{760} ]

Where:

• (N_a) = adjusted number of containers
• (N) = initial number of containers
• (P_{ambient}) = enclosure pressure (mm Hg)

4. Enclosure Volume Calculation (Clause 7.3.1)

[ V_{Mn} = V_g - V_s ]

• (V_{Mn}): Maximum net volume (m³)
• (V_g): Gross enclosure volume (m³)
• (V_s): Volume

IS 15835 - Venting Arrangement: Key Points & Formulas

1. Venting Arrangement (Clause 6)

• Vents must be located as high as possible in the enclosure to allow safe release of HCFC-125 vapor.
• Enclosure strength and allowable pressure must comply with relevant building codes.
• Vent sizing depends on enclosure volume and expected pressure rise during discharge.

2. Enclosure Volume Calculation (Clause 7.3.1)

• Net enclosure volume accounts for structural and occupancy volumes impermeable to gas:

[ V_{Mn} = V_g - V_s ]

Where:

• (V_{Mn}) = Maximum net volume (m³)
• (V_g) = Gross enclosure volume (m³)
• (V_s) = Volume of permanent objects (m³)

If occupancy objects volume (V_o < 25%) of (V_{Mn}), it can be ignored.

3. Design Concentration (Clause 8)

• Minimum HCFC-125 design concentrations:

• Use highest concentration if multiple hazard classes exist.

4. Atmospheric Correction Factor (Clause 8f, Table 8)

Adjust agent quantity for altitude:

[ N_a = N \times \frac{P_{ambient}}{P_{sea\ level}} ]

5. Pipe Sizing (Clause 12.3, Table 9)

| Pipe Dia. (mm) | Max Flow Rate (kg/s) for Length >

IS 15835 Key Points on Extinguishing Agent Supply (HCFC-125):

1. Quantity Requirements (Clause 7.1)

• Main quantity: Sufficient for largest single or communicating hazard.
• Reserve quantity: Equal to main quantity; may vary if replenishing >7 days.
• Uninterrupted protection: Both main and reserve connected for quick change-over.
• Adjustments: Compensate for openings, ventilation, air receivers, altitude, etc.
• Design concentration must not exceed LOAEL.

2. Design Concentration (Clause 8.6)

• Class B fuels: 8.6% (Heptane) + 30% safety = 11.3%
• Class C (electrical): 6.6% + 20% safety = 7.9%
• For other fuels, use lab-tested extinguishing concentration + 20-30% safety.
• Use highest concentration if multiple hazards.

3. Atmospheric Correction Factor (Altitude Adjustment)

[ N_a = N \times \frac{P_{altitude}}{P_{sea\ level}} ]

(Refer Table 8 for full values)

4. Enclosure Volume Calculation (Clause 7.3.1)

[ V_{Mn} = V - V_s ]

• (V): Gross enclosure volume (m³)
• (V_s): Volume of permanent objects impermeable to gas (m³)

5. Mass of HCFC-125 Required (Table 7)

• Mass per m³ depends on temperature and design concentration.
• Example at 20°C for 8% vol: approx. 0.441 kg/m³

Summary Formula for Number of Containers:

[ N_a = N \times \text{Atmospheric Correction Factor} ]

Where:

IS 15835: Design Concentration Key Points

1. Minimum Design Concentrations (Clause 8.6):

Note: For mixed hazards, use the highest required concentration.

2. Total Flooding Quantity (Clause 7.2):

[ M = V \times S \times \frac{100}{100 - C} ]

Where:

• (M) = total HCFC-125 quantity (kg)
• (V) = net enclosure volume (m³)
• (C) = design concentration (%)
• (S = K_1 + K_2 \times T) (temperature correction)
• (K_1 = 0.1825), (K_2 = 0.0007), (T) = min enclosure temp (°C)

3. Atmospheric Correction Factors (Table 8):

Adjusted containers:
[ N_a = N \times \frac{P_{avg}}{P_{sea-level}} ]

Where:

• (N_a) = adjusted number

Post Discharge Scenario: IS 15835 Key Points & Formulas

1. Concentration Requirements (Clause 9):

• Within 1 min of discharge start, concentration at ≤1 m above floor or top hazard must be within ±1% of design concentration.
• At 10 min, concentration must be ≥ 80% of design concentration.

2. Design Concentration (Clause 8.6):

• Class B fuels (Heptane):
  [ C_{design} = 8.6% \times 1.3 = 11.3% ]
• Class C (Electrical):
  [ C_{design} = 6.6% \times 1.2 = 7.92% ]
• Use highest concentration if multiple hazards.

3. Agent Quantity Calculation (Clause 7.2):
[ M = V \times C \times S \times \frac{100}{100 - C} ]
Where:

• (M) = agent mass (kg)
• (V) = enclosure volume (m³)
• (C) = design concentration (%)
• (S = K_1 + K_2 \times T) (temperature correction)
• (K_1 = 0.1825), (K_2 = 0.0007), (T) = min enclosure temp (°C)

4. Atmospheric Correction Factor (Clause 8.6(e), Table 8):
Adjust number of containers (N_a) for altitude:
[ N_a = N \times \frac{P_{altitude}}{P_{sea\ level}} ]
Use Table 8 for (P_{altitude}) and correction factor.

Summary:

• Ensure design concentration with safety factors (20-30%).

IS 15835 Key Specifications for Application Rate, Duration & Discharge Time

1. Application Rate (Clause 10.1)

• Based on quantity of HCFC-125 (Clause 7.2(a)) and duration of discharge (Clause 9(b)).
• Must ensure design concentration is achieved within 1 min and maintained ≥ 80% for 10 min.

2. Duration of Discharge & Discharge Time (Clause 10.1 & 13.1)

• Use approved hydraulic calculation methods to predict:

  • Pipe sizes
  • Nozzle pressure
  • Agent flow rate
  • Discharge per nozzle
  • Discharge time

• Accuracy requirements:

  • Agent weight discharged: within -5% to +10% of predicted.
  • Discharge time: predicted ≈ actual.
  • Nozzle pressure: within acceptable min/max for uniform agent distribution.

3. Pipe Sizing (Table 9, Clause 12.3)

4. Design Concentration & Atmospheric Correction (Clause 8.6 & Table 8)

• Design concentration includes safety factors (e.g., 11.3% for Class B fuel hazards).
• Adjust agent quantity for altitude using:

[ N_a = N \times \frac{P_{ambient}}{P_{sea level}} ]

Where:

• (N_a) = adjusted containers
• (N) = initial containers
• (P_{ambient}) = enclosure pressure (from Table 8)
• (P_{sea level} = 760 \text{ mm Hg})

IS 15835: Distribution System Key Points

1. Pipe Sizing (Clause 12.3 & Table 9)

• Pipe diameter selection depends on flow rate and pipe length.
• Too small diameter → high pressure loss; too large → low velocity & pressure drop.
• Use Table 9 as a guide for max flow rates (kg/s) for pipe sizes (mm):

2. Pressure Requirements (Clause 12.1)

• Pipes must withstand max expected pressure at max storage temperature.
• Storage containers pressurized with nitrogen at 2.5 MPa ±5% or 4.2 MPa +5% at 21±1°C.
• Containers must have reliable pressure and temperature indicators.

3. Atmospheric Correction (Clause 8.6 & Table 8)

• Adjust HCFC-125 quantity for altitude using atmospheric correction factor:

IS 15835: Hydraulics of the System - Key Formulas, Tables & Specifications

1. Pipe Sizing (Clause 12.3 & Table 9)

• Pipe diameter selection depends on flow rate and pipe length.
• Avoid too small bore (excess pressure loss) or too large bore (low velocity).
• Use Table 9 as a guide for pipe size vs flow rate (kg/s) for different pipe lengths:

2. Hydraulic Calculation Accuracy (Clause 13.1)

• Weight of agent discharged: ±5% to +10% accuracy.
• Discharge time prediction must match actual.
• Nozzle pressure must be within min/max limits for uniform agent distribution.
• Use approved hydraulic calculation software.

3. Piping Specifications (Clause 4.2)

• Operating pressure: 4.2 MPa, design pressure: 6.58 MPa at 55°C.
• Pipes: Carbon steel (galvanized inside/outside) or stainless steel.
• Compliance with IS 15493 for pressure resistance.

4. Nozzle Placement (Clause 4.1)

• Max nozzle height: 4.1 m; if higher, add rows.
• Min nozzle height: 0.46 m above floor.
• Max distance between nozzles: 6 m; max distance to wall: 3 m.
• Concealed spaces must have nozzles.

Summary Diagram of System Layout

graph TD

IS 15835: Commissioning and Acceptance Testing of HCFC-125 Systems

Key Points from Clause 14 and Related Clauses:

• Commissioning Standard:
  Commission the HCFC-125 total flooding system as per Clause 9 of IS 15493 to prove system performance.

• Acceptance Criteria (Table 14.1):
  The system must meet performance requirements, including:

  • Concentration uniformity within ±1% by volume at 1 m above floor/top hazard within 1 min of discharge start.
  • Concentration ≥ 80% of design concentration at 10 min post-discharge.

• Design Concentration (Clause 8.6):

  • Class B fuels: Minimum 11.3% HCFC-125 by volume (8.6% extinguishing + 30% safety factor).
  • Class C (electrical): 6.6% + 20% safety factor.
  • Use highest concentration if multiple hazards exist.

• Atmospheric Correction Factor (Table 8):
  Adjust agent quantity for altitude:

Formula:
[ N_a = N \times \frac{P_{ambient}}{P_{sea-level}} ]

Where:

• (N_a) = adjusted number of containers
• (N) = initial number of containers
• (P_{ambient}) = enclosure pressure at altitude
• (P_{sea-level}) = standard sea level pressure (760 mm Hg)

Summary Diagram of Commissioning Flow

flowchart TD
    A[System Installation] --> B[Commissioning as per IS 15493 Clause 9]
    B --> C[Discharge Test]
    C --> D{Concentration within ±1% at 1 min?}
    D -- Yes --> E{Concentration ≥ 80% at 10 min?