Specification For Fire Bells

IS 928 - Scope & Key Specifications

Scope:
IS 928 covers the standard requirements for fire bells, focusing on materials, dimensions, and acoustic performance.

Key Specifications

• Sound Pressure Level:

  • Minimum 100 dB at 5 m distance
  • Measured using an impact noise analyzer with a time constant of 0.01 s
  • Strike frequency: 600 to 1000 Hz
  • Impact by mild steel ball with momentum = 1 kg·m/s (100,000 g·cm/s)

• Measurement Conditions:

  • Open ground with ambient noise at least 10 dB below bell sound
  • No obstacles within 12 m radius
  • Anechoic chambers allowed if sound pressure variation ≤ ±1 dB
  • Bell and microphone mounted at 1 m height

• Bell Dimensions:

  • As per Fig. 1 (fire bell shape)
  • Tolerance: ±2 mm

Rounding off Results (Clause 0.4)

• Follow IS 2-1960 for rounding off test results
• Retain the same significant figures as specified values

Summary Table

flowchart LR
    A[Fire Bell] --> B[Struck by Steel Ball]
    B --> C[Sound Pressure ≥ 100 dB at 5m]
    C --> D[Measured by Impact Noise Analyzer]
    D --> E[Frequency 600-1000 Hz]
    E --> F[Measurement Conditions]
    F --> G[Open Ground or Anechoic Chamber]

This summarizes the scope and key requirements from IS 928 for fire bells.

IS 928 - Materials Specifications Summary

• Bell Metal (Shell):

  • Conforms to IS 306-1968 (Tin Bronze Ingots and Castings).
  • Composition: Tin 20-22%, Copper 78-80%.
  • Alternative: Brass as per IS 292-1961.

• Mild Steel (Brackets & Other Items):

  • Conforms to IS 1977-1951 (Specification for Mild Steel).

• Rounding Off Values:

  • Follow IS 2-1960 for rounding test/analysis results.
  • Retain the same number of significant places as specified values.

Key Material Properties (Typical values):

flowchart LR
    A[Materials] --> B[Bell Metal (IS 306)]
    A --> C[Mild Steel (IS 1977)]
    B --> D[Tin 20-22%]
    B --> E[Copper 78-80%]
    C --> F[Brackets & Other Items]

This ensures materials meet durability and performance for bell manufacturing under IS 928.

IS 928 - Key Construction Specifications and Formulas

1. Materials

• Leather for Strap: Must conform to IS: 581-1968 (Vegetable tanned hydraulic leather).
• Mild Steel for Bracket & Items: Must conform to IS: 1977-1951 (Structural steel, ordinary quality).

2. Sound Test for Bell

• Impact: Mild steel ball with momentum = 100,000 g·cm/s (1 kg·m/s)
• Sound Pressure Level: ≥ 100 dB at 5 m distance
• Frequency Range: 600 to 1,000 Hz
• Measurement Conditions:
  • Open ground: Ambient noise ≥ 10 dB below bell output, no obstacles within 12 m.
  • Anechoic chamber: Sound pressure variation within ±1 dB.
  • Bell and microphone height: 1 m above ground.

3. Construction Details (Fig.1 Summary)

• Includes hanging bracket and spring to keep clapper in position.
• All dimensions in millimeters.

Summary Table for Materials

flowchart LR
    A[Leather Strap] -->|IS:581-1968| B[Vegetable Tanned Leather]
    C[Mild Steel Bracket] -->|IS:1977-1951| D[Structural Steel]
    E[Bell Impact Test] --> F[100 dB @ 5m]
    F --> G[Momentum = 1 kg·m/s]
    F --> H[Frequency 600-1000 Hz]

This ensures compliance with IS 928 construction and acoustic performance requirements.

IS 928 Key Specifications: Dimensions and Mass of Fire Bell

• Dimensions (Clause 3.1):

  • Shape and size as per Fig. 1 (not shown here).
  • Tolerance: ±2 mm on all dimensions.
  • All dimensions in millimeters.

• Mass (Clause 4.1):

  • Mass of the bell shell = 10 ± 1 kg.

• Sound Pressure Level (Clause 6.1):

  • Minimum peak sound pressure level = 100 dB at 5 m distance.
  • Strike by mild steel ball with momentum = 1 kg·m/s (100,000 g·cm/s).
  • Frequency range of strike tone = 600 to 1000 Hz.

• Test Setup Notes:

  • Bell and microphone at 1 m height above ground.
  • Open ground test: no obstacles within 12 m radius; ambient noise ≥10 dB below signal.
  • Anechoic chamber: sound pressure variation within ±1 dB.

Summary Table

This ensures consistent acoustic performance and dimensional accuracy for fire bells per IS 928.

IS 928 – Workmanship and Finish (Clause 5)

• Casting Quality:

  • Must be sound, free from:
    • Sharp edges
    • Pits
    • Blowholes
    • Scales
    • Other imperfections
  • No repairs or fillings to conceal defects allowed.

• Surface Finish:

  • Unmachined surfaces to be dressed and finished smooth.
  • All sharp edges removed.

• Corrosion Protection:

  • Mild steel fittings require a suitable anticorrosive treatment.

• Mass Specification:

  • Shell mass = 10 ± 1 kg (Clause 4.1).

Summary Table for Workmanship

This ensures structural integrity and durability of cast components per IS 928.

IS 928: Performance Test for Fire Bells

Key Specifications (Clause 6.1)

• Test Setup: Bell struck by a mild steel ball with momentum = 100,000 g·cm/s (1 kg·m/s)
• Measurement Distance: 5 m from bell
• Minimum Sound Pressure Level: ≥ 100 dB
• Frequency Range of Strike Tone: 600 to 1000 Hz
• Measurement Conditions:
  • Open ground: Ambient noise ≥ 10 dB below bell sound, no obstacles within 12 m, no acoustic focusing.
  • Anechoic chamber: Sound pressure variation within ±1 dB.
• Equipment Setup: Bell and microphone at 1 m height above ground.
• Instrument: Impact noise analyzer with 0.01 sec time constant.

Additional Notes:

• Bell surfaces must be sound, smooth, free from defects (Clause 5.1).
• Measurements should follow rounding rules per IS 2-1960.

Summary Table:

flowchart LR
    A[Strike Bell with Steel Ball] --> B[Sound Pressure Generated]
    B --> C[Measure at 5 m Distance]
    C --> D{Sound Level ≥ 100 dB?}
    D -- Yes --> E[Test Passed]
    D -- No --> F[Test Failed]

This ensures the bell produces adequate audible alert per IS 928.

IS 928: Marking Specifications for Fire Bells

Key Marking Requirements (Clause 7.1)

Each fire bell must be clearly and permanently marked with:

• Manufacturer's name or trade-mark
• Year of manufacture
• Type of materials

Acoustic Performance (Clause 6.1)

• Minimum peak sound pressure level: 100 dB at 5 m distance
• Strike method: Mild steel ball with momentum 100,000 g·cm/s (1 kg·m/s)
• Frequency range of strike tone: 600 to 1,000 Hz
• Measurement conditions:
  • Open ground with ambient noise ≥10 dB below bell output, no obstacles within 12 m
  • Anechoic chamber with ±1 dB sound pressure variation

Measurement Setup

• Bell and microphone height: 1 m above ground
• Time constant of impact noise analyser: 0.01 second

Rounding Off Results (Clause 0.4)

• Follow IS 2-1960 for rounding off test results, matching significant figures to specified values.

flowchart LR
    A[Fire Bell] --> B[Marking]
    B --> C[Manufacturer's name/trade-mark]
    B --> D[Year of manufacture]
    B --> E[Type of materials]
    A --> F[Acoustic Test]
    F --> G[Strike with steel ball (1 kg·m/s)]
    F --> H[Measure sound pressure ≥100 dB @ 5m]
    F --> I[Frequency 600-1000 Hz]

This ensures traceability and compliance with IS 928 standards.