Gaseous Fire Extinguishing Systems - General Requirements

IS 15493: Scope - Key Formulas, Tables, and Specifications

Notations (Clause 2.1)

Agent Densities (kg/m³)

Leakage Rate Formula (General form)

[ Q = C \times P^N ]

Where:

• Q = Air leakage rate (m³/s)

• C = Flow coefficient

• P = Pressure difference (Pa)

• N = Slope of the graph (empirical)

Safety Concentrations (from Table 6.2)

IS 15493 - Definitions and Notations (Clause 2.1 & related)

Key notations for clean agent fire suppression systems:

Agent Densities (kg/m³)

Notes:

• Discharge coefficient (K) varies based on leakage opening nature.
• Leakage

IS 15493: General Requirements - Key Formulas, Tables & Specs

1. Notations (Clause 2.1, Table D-2.1)

Agent Densities:

• Air: 1.202 kg/m³
• HCFC Blend A: 3.84 kg/m³
• HFC-227ea: 7.26 kg/m³
• IG-541 & IG-55: 1.41 kg/m³

2. Key Parameters (Clause 9.81)

3. Important Formulae

• Leakage Rate Correction:

[ 2M = 2m \times \sqrt{\frac{RM}{RA}} ]

• Equivalent Leakage Area:

[ ELA = \frac{Q}{C \sqrt{2 \times P / RM}} ]

• **Retention Time (

IS 15493: Application and Limitations - Key Formulas & Specifications

1. Application (Clause 4.2)

• Applicable for gaseous fire suppression systems in enclosed spaces.
• Suitable for enclosures where agent concentration and retention time ensure fire suppression.
• Enclosure geometry, leakage rates, and agent properties must be considered.

2. Limitations (Clause 4.3)

• Not suitable for open or poorly sealed spaces.
• Effectiveness reduces with high leakage or ventilation.
• Agent density and temperature differences affect performance.

3. Key Formulas

• Air Leakage Rate:

[ Q = C \times P^N ]

Where:

• (Q) = air leakage rate (m³/s)

• (C) = flow coefficient

• (P) = pressure difference (Pa)

• (N) = slope of graph (dimensionless)

• Agent/Air Mixture Leakage Rate Correction:

[ 2_M = 2_m \times \sqrt{\frac{R_M}{R_A}} ]

Where:

• (2_m) = uncorrected leakage rate (m³/s)

• (2_M) = corrected leakage rate (m³/s)

• (R_M) = density of agent/air mixture (kg/m³)

• (R_A) = density of air (1.202 kg/m³)

• Equivalent Leakage Area (ELA):

[ ELA = \frac{Q}{K \sqrt{2gH}} ]

Where:

• (K) = discharge coefficient (0.61 to 1)
• (g) = gravitational acceleration (9.81 m/s²)
• (H) = height of enclosure (m)

4. Agent Densities (kg/m³) [Clause 2.1]

Summary:

• Ensure enclosure tightness (low leakage).
• Use agent density and **temperature

IS 15493: Safety Precautions for Total Flooding Systems

Key Tables & Formulas

1. Toxicity Levels of Clean Agents (Table 2)

2. Minimum Safety Precautions (Table 2A)

¹ Concentrations above LOAEL are not permitted in occupied areas.

Additional Safety Specifications

• Exit routes: Must be kept clear with emergency lighting and signage.
• Doors: Outward swinging, self-closing, openable from inside even if locked outside.
• Alarms: Continuous visual and audible alarms at entrances/exits until area is safe.
• Pre-discharge alarms: Distinctive and immediate upon fire detection.
• Ventilation: Prompt forced ventilation post-discharge to dissipate hazardous atmospheres.
• Training: Personnel must be trained for correct response during system operation.

Important Notes

• System recalculation is mandatory if enclosure volume or contents change to maintain agent concentration within NOAEL/LOAEL limits.

IS 15493: System Components and Materials - Key Formulas & Tables

1. Notations (Clause 2.1, Table D-2.1)

2. Agent Densities

3. Leakage Rate Correction

• Uncorrected leakage rate: ( 2m ) (m³/s)
• Corrected leakage rate: ( 2M ) (m³/s)

4. Key Parameters

5. Pre-engineered System (Clause 12.3)

• Single container with max two nozzles.
• Small piping

IS 15493 Installation Requirements: Key Formulas, Tables & Specs

1. Completion Certificate & Documentation (Clause 10.11)

• Installer must provide:
  • Completion certificate.
  • Full instructions, calculations, and as-installed drawings.
  • Statement of compliance with IS 15493.
  • Details of any deviations.
  • Design concentrations and test reports (e.g., door fan test).

2. Hydraulic Flow Calculations (Clause 11 & 2.1)

• Key Notations:

• Agent Densities (kg/m³):

3. Pipe Installation & Supports (Clause 8.2.4)

• Avoid restrictions due to debris or improper fabrication.
• Ream pipe ends after cutting.
• Use secure supports in explosion-prone areas.
• Max distance between pipe supports depends on pipe diameter and agent mass.

IS 15493: Storage Containers & Accessories — Key Points

1. Agent Storage (Clause 8.1.2)

• Containers must be specific to the agent and operate at ambient temperature.
• Fill density and super-pressurization per manufacturer specs.
• Temperature limits: -21°C to 55°C; use heating/cooling if needed.
• Containers must comply with Department of Explosives, Nagpur.
• Permanent nameplate marking as per Table 4.
• Pressure monitoring for refillable super-pressurized containers.
• Containers on a common manifold must follow Table 5.

2. Markings on Containers (Table 4)

3. Common Manifold Arrangement (Table 5)

4. Storage Container Arrangement (Clause 8.1.3)

• Easy access for inspection, testing, recharging.
• Preferably outside, near protected enclosure.
• Protection from weather, mechanical, chemical damage.
• Adequate mounting for airflow and servicing.
• Non-return valves in manifold systems.
• Brackets designed for max mass, vibration, shock.
• Reserve containers easily changeable.
• Gas detectors recommended if leakage hazard exists.

Summary Diagram: Container Arrangement & Marking

flowchart TD
    A[Agent Storage] --> B[Specific Containers]
    B --> C[Temperature: -21°C to 55°C]
    B --> D[Marking per Table 4]
    B --> E[Pressure Monitoring]
    A --> F[Common Manifold]
    F --> G[Halocarbon: Identical Containers]
    F --> H[Inert Gas: Different Sizes Allowed]
    A --> I[Storage Arrangement]
    I --> J[Easy Access & Maintenance]
    I --> K[

IS 15493: Power Supply & Electrical Wiring Key Points

1. Wiring Installation (Clause 10.3.1)

• Wiring must comply with national electrical standards (e.g., IS 732 for wiring).
• AC and DC wiring must not share conduits unless shielded & grounded to prevent interference.
• Follow system drawings strictly for layout and routing.

2. Power Source Requirements (Clause 9.2.2 & 10.7)

• Provide primary power source with 24-hour minimum standby (battery or UPS).
• Standby must ensure continuous operation of:
  • Detection
  • Signalling
  • Control
  • Actuation systems

3. Typical Power Supply Specifications

4. Important Formula: Battery Capacity

[ \text{Battery Capacity (Ah)} = \frac{\text{Load Current (A)} \times \text{Backup Time (h)}}{\text{Discharge Efficiency}} ]

flowchart LR
    A[Primary Power Source] --> B[Control Panel]
    B --> C[Detection System]
    B --> D[Signalling System]
    B --> E[Actuation System]
    F[Standby Power Source (24h)] -.-> B

Summary: Ensure separate, shielded wiring for AC/DC, reliable primary + 24h standby power, and adherence to national wiring standards for safety and system reliability.

IS 15493: Commissioning and Acceptance Testing – Key Points

1. Completion Certificate (Clause 10.11)

• Installer must provide:
  • Completion certificate.
  • Full instructions, calculations, and as-installed drawings.
  • Statement confirming compliance with IS 15493.
  • Details of any deviations.
  • Design concentrations and reports of additional tests (e.g., door fan test).

2. Minimum Apparatus for Commissioning (Clause 1.2)

• Fan unit: Variable speed, seals access opening, ≥25 Pa differential pressure.
• Pressure devices: Two units (enclosure differential pressure, fan flow pressure).
• Flexible tubing: For pressure connections.
• Smoke pencils/generator: To detect leaks.
• Thermometers: Measure ambient temperature.
• Warning signs: For pressure test safety.

3. Testing Requirements (Clause 10.2.2 to 10.2.9)

• Verify installation integrity.
• Confirm system operation without time delays for detection (Clause 9.6.3).
• Perform pressure and leakage tests using fan unit and smoke.
• Check system hydraulic flow calculations (Clause 11).

Typical Pressure Test Setup

flowchart LR
    A[Fan Unit] -->|Creates Pressure| B[Enclosure]
    B -->|Pressure Measurement| C[Pressure Gauges]
    B -->|Leak Detection| D[Smoke Generator]
    E[Ambient Thermometers] --> B

Summary Table: Apparatus and Purpose

This ensures system integrity and compliance before handover.

IS 15493: Hydraulic & Pneumatic Considerations - Key Formulas & Tables

1. Notations (Clause 2.1)

• Q = Air leakage rate (m³/s)
• C = Flow coefficient
• P = Pressure in enclosure (Pa)
• RM = Density of agent/air mixture (kg/m³)
• RA = Density of air (1.202 kg/m³)
• RG = Density of agent (varies by agent)

2. Minimum Design Working Pressure for Piping (Clause 8.2.2.1)

Note: Super-pressurized with nitrogen

3. Pressure Drop Calculation (Clause 11.4)

• Use two-phase flow equations for liquefied gases.
• Use single-phase flow equations for non-liquefied gases.
• Iterative calculation involving friction factors, pressure, and density.
• Typically requires computer programs for accuracy.

4. Leakage Rate Correction (Clause 9.81)

• Corrected leakage rate ( Q_M ) depends on:

[ Q_M = Q_{2m} \times \sqrt{\frac{R_M \times T_L}{R_A \times T_F}} ]

IS 15493: Engineered & Pre-Engineered Systems - Key Points

1. Pre-Engineered Systems (Clause 12.3)

• Single container with max 2 nozzles + small piping.
• Modular units cover larger areas by multiplication.
• No flow calculations needed if within approved limits.

2. System Flow Calculations (Clause 11.1)

• Calculations at nominal agent storage temp = 21°C.
• Must be validated by accredited authority.
• Variations in temp affect flow conditions.
• Use manufacturer's limits strictly.

3. Physical Properties (Clause 13 & Table 2.1)

4. Key Notations for Flow Calculations

5. Example Flow Formula (Generic form)

[ Q = C \times P^N \times \sqrt{\frac{RM}{RA}} ]

Where:

• (Q) = leakage flow rate
• (C) = flow coefficient
• (P) = pressure difference
• (N) = empirical slope
• (RM), (RA) = densities of mixture and air

flowchart LR
    A[Pre-Engineered Unit] --> B[Single Container]
    B --> C[Max 2 Nozzles]
    B --> D[Small

IS 15493: Physical Properties of Clean Agents

Key Tables & Specifications

1. Inert Gas Agents (Table 9)

2. Halocarbon Agents (Table 10)

Training and Personnel Competency (IS 15493 - Clause 14)

Key Requirements:

• Clause 14.1: All personnel involved in operation, maintenance, testing, or inspection of fire extinguishing systems must be continuously and adequately trained.
• Clause 14.2: Personnel working in enclosures protected by gaseous extinguishants must be fully conversant with system operation, use, and safety.

Important Physical Properties (For Training Reference)

Leakage Rate Calculation (Clause 9.81)

[ Q = C \times A \times \sqrt{\frac{2 \times \Delta P}{\rho}} ]

Where:

• ( Q ) = air leakage rate (m³/s)
• ( C ) = flow coefficient
• ( A ) = leakage area (m²)
• ( \Delta P ) = pressure difference (Pa)
• ( \rho ) = density of air or agent-air mixture (kg/m³)

Summary for Training Programs

• Understand agent physical properties (Tables 9 & 10) for safe handling.
• Operate and maintain systems per manufacturer and IS 15493 guidelines.
• Safety protocols for personnel in protected enclosures.

IS 15493: List of Referenced Indian Standards – Key Points

IS 15493 references multiple Indian Standards essential for design and implementation of fire extinguishing systems using gaseous agents. While the exact list is not given in your context, typical referenced standards include:

• IS 2190: Code of practice for selection, installation, and maintenance of automatic fire detection and alarm systems.
• IS 15105: Specification for carbon dioxide fire extinguishing systems.
• IS 3844: Specification for dry chemical powder fire extinguishers.
• IS 2878: Specification for foam fire extinguishers.
• IS 2189: Specification for fire extinguishers (general requirements).
• IS 1646: Specification for fire extinguishing systems using halogenated hydrocarbons.

Important Notes on Agent Flow & Pressure (Clauses E-1 to E-10)

• Pressure in storage containers drops during discharge; vapor-liquid equilibrium assumed.
• Two-phase flow (liquid + vapor) in pipes causes variable pressure drops.
• Density of agent varies during discharge; temperature drops due to pressure fall.
• Initial vaporization delays liquid flow to nozzles.
• Proper pipe sizing avoids phase separation and flow issues.
• Average nozzle pressure is taken at half liquid discharge for calculations.

Typical Formula for Pressure Drop in Two-Phase Flow (Conceptual)

[ \Delta P = f \frac{L}{D} \frac{\rho v^2}{2} ]

• ( \Delta P ) = pressure drop
• ( f ) = friction factor (variable due to two-phase flow)
• ( L ) = pipe length
• ( D ) = pipe diameter
• ( \rho ) = density of two-phase mixture
• ( v ) = velocity of flow

Summary Table: Agent Flow Characteristics

For detailed referenced IS

IS 15493: Safety Information & Decomposition Products Summary

Key Safety Specifications (Clause 6.1 & Annex B)

• Toxicity Limits (Table 2):
  • NOAEL (No Observed Adverse Effect Level), LOAEL (Lowest Observed Adverse Effect Level), LC50 (Lethal Concentration 50%) in % volume for agents like HCFC Blend A, IG-541, IG-55, IG-100, IG-01.
• Decomposition Products:
  • Halocarbon agents decompose above 480°C, producing hazardous hydrogen fluoride (HF) in presence of hydrogen (from water vapor or fire).
  • HF has a sharp acrid odor at a few ppm, serving as a warning but creating noxious atmosphere.
  • Longer exposure to >482°C increases toxic gas concentration.
• Non-liquefied agents (e.g., inert gases) do not decompose significantly, but fire byproducts like CO can still be hazardous.

Safety Precautions (Table 2A)

• Concentrations above LOAEL are not permitted in occupied areas.

Physical Properties (Tables 9 & 10)

• Molecular weight, boiling/freezing points, critical temperature & pressure, heat of vaporization, dielectric strength, and water solubility are tabulated for inert gases and halocarbon agents.

Important Notes:

• Avoid unnecessary exposure; ensure egress in 30s if above NOAEL.
• Use pre-discharge alarms and ventilation to clear toxic atmospheres.
• Personnel must be trained on system operation and hazards (Clause 14.2).

flowchart TD
    A[Fire Occurs] --> B[Agent Discharged]
    B --> C{Temperature > 480°C?}
    C -- Yes --> D[Halocar

IS 15493: Two-Phase Flow for Liquefied Halocarbon Gases (Annex E, Clause 11.8.3)

Key Points:

• Two-phase flow applies to liquefied halocarbon gases; pressure drop calculations must use two-phase flow equations.
• For non-liquefied gases, single-phase flow equations suffice.
• Empirical friction factors and constants depend on pressure and density.
• Iterative numerical methods or computer programs are needed due to equation complexity.

Important Notations (Clause 2.1):

Agent Densities (kg/m³):

Typical Two-Phase Pressure Drop Calculation Outline:

[ \Delta P = f(\rho, v, D, L, x) ]

Where:

• (\rho) = mixture density (kg/m³)
• (v) = velocity (m/s)
• (D) = pipe diameter (m)
• (L) = pipe length (m)
• (x) = vapor quality (mass fraction vapor)

Note: Empirical correlations such as Lockhart-Martinelli or homogeneous flow models are often used.

Summary Flowchart for Pressure Drop Calculation:

flowchart TD
    A[Start: Define Gas & Conditions] --> B[Determine Phase: Single or Two-Phase]
    B -->|Single-Phase