Specification For Fire Bells
1984 Edition

Overview of Scope and Main Specifications

Scope:
This specification defines the essential criteria for fire alarm bells, emphasizing the materials used, dimensional details, and acoustic capabilities.

Principal Requirements

• Minimum Sound Pressure Level:

  • At least 100 dB measured at a 5-meter distance
  • Sound measurement conducted with an impact noise analyzer set to a 0.01-second time constant
  • Strike frequency range: 600 to 1000 Hz
  • Impact delivered by a mild steel ball with momentum of 1 kg·m/s (100,000 g·cm/s)

• Testing Conditions:

  • Conducted in open areas with ambient noise at least 10 dB lower than bell output
  • No obstructions within a 12-meter radius
  • Use of anechoic chambers permitted if sound pressure variation does not exceed ±1 dB
  • Both bell and microphone positioned at a height of 1 meter

• Bell Dimensions:

  • As illustrated in Fig. 1 (typical fire bell profile)
  • Allowed dimensional tolerance: ±2 mm

Rules for Rounding Results (Clause 0.4)

• Adhere to IS 2-1960 guidelines for rounding off test data
• Preserve the same number of significant digits as the specified values

Summary Table

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

This section summarizes the scope and fundamental requirements as per the specification.

Material Specifications According to the Standard

• Bell Metal (Shell):

  • Must comply with IS 306-1968 (Specification for tin bronze ingots and castings).
  • Composition: 20-22% Tin, 78-80% Copper
  • Acceptable alternative: Brass conforming to IS 292-1961.

• Mild Steel Components:

  • Should meet IS 1977-1951 (Specification for mild steel).

• Rounding Rules:

  • Apply IS 2-1960 for test result rounding
  • Maintain the specified number of significant figures.

Typical Mechanical Properties

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

Ensuring materials meet these standards guarantees durability and performance in bell manufacturing.

Manufacturing Specifications and Acoustic Testing

1. Materials Used

• Leather Strap: Should comply with IS 581-1968 (Vegetable tanned hydraulic leather).
• Mild Steel Parts: Must meet IS 1977-1951 (Ordinary structural steel).

2. Acoustic Testing Parameters

• Striking Method: Impact by mild steel ball with momentum = 1 kg·m/s (100,000 g·cm/s)
• Required Sound Level: Not less than 100 dB at 5 meters
• Frequency Band: 600 to 1,000 Hz
• Testing Conditions:
  • Open ground with ambient noise at least 10 dB below bell sound, clear radius of 12 meters
  • Anechoic chamber with sound pressure variation within ±1 dB
  • Bell and microphone placed at 1 meter height

3. Construction Particulars (Refer Fig.1)

• Includes hanging brackets and a spring mechanism to secure the clapper
• All measurements are in millimeters

Materials Summary Table

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

This ensures compliance with manufacturing and acoustic standards.

Standardized Dimensions and Mass for Fire Bells

• Dimensions (Clause 3.1):

  • Shape and size as outlined in Fig. 1 (not included here)
  • Permitted tolerance: ±2 mm
  • Units: millimeters

• Mass (Clause 4.1):

  • Bell shell mass specified as 10 ± 1 kg

• Acoustic Performance (Clause 6.1):

  • Minimum peak sound pressure: 100 dB at 5 m
  • Impact by mild steel ball with momentum of 1 kg·m/s (100,000 g·cm/s)
  • Strike tone frequency between 600 and 1000 Hz

• Test Setup:

  • Bell and microphone positioned at 1 m above ground
  • Open ground environment free of obstacles within 12 m radius and ambient noise at least 10 dB lower
  • Anechoic chamber allowed with sound variation within ±1 dB

Summary Table

This guarantees dimensional accuracy and consistent sound output.

Workmanship and Surface Finish Requirements (Clause 5)

• Casting Quality:

  • Must be sound and free from defects such as:
    • Sharp edges
    • Pitting
    • Blowholes
    • Scale deposits
    • Other imperfections
  • No repairs or filling to mask defects are permitted

• Surface Finish:

  • Unmachined areas should be smoothly dressed and finished
  • All sharp edges must be removed

• Corrosion Protection:

  • Mild steel fittings require appropriate anti-corrosion treatment

• Mass Compliance:

  • Bell shell mass to be maintained at 10 ± 1 kg (Clause 4.1)

Workmanship Summary Table

These measures ensure the bell’s structural integrity and durability.

Performance Testing Protocol for Fire Bells

Acoustic Test Parameters (Clause 6.1)

• Striking Device: Mild steel ball with momentum of 1 kg·m/s (100,000 g·cm/s)
• Measurement Distance: 5 meters from the bell
• Minimum Sound Pressure Level: At least 100 dB
• Frequency Range: 600 to 1000 Hz
• Testing Environment:
  • Open ground with ambient noise at least 10 dB lower than the bell sound, no obstructions within 12 meters
  • Anechoic chamber with sound variation within ±1 dB
• Equipment Setup: Bell and microphone positioned at 1 m height
• Instrumentation: Impact noise analyzer with a time constant of 0.01 seconds

Additional Considerations:

• Bell surfaces must be free from defects and smooth (Clause 5.1).
• Test results should be rounded according to IS 2-1960.

Summary Table

flowchart LR
    A[Bell Struck by Steel Ball] --> B[Sound Pressure Generated]
    B --> C[Measured at 5 m]
    C --> D{Sound Level ≥ 100 dB?}
    D -- Yes --> E[Pass]
    D -- No --> F[Fail]

This ensures the bell’s sound is sufficiently loud for emergency notification.

Marking Requirements for Fire Bells (Clause 7.1)

Each fire bell must bear a clear, permanent marking including:

• Manufacturer’s name or trademark
• Year of manufacture
• Material type used

Acoustic Requirements Reminder (Clause 6.1)

• Minimum peak sound pressure level of 100 dB at 5 meters
• Strike method using mild steel ball with momentum of 1 kg·m/s
• Frequency range between 600 and 1000 Hz
• Testing conditions ensuring ambient noise and obstruction limits

Measurement Setup

• Bell and microphone both mounted at 1 meter height
• Impact noise analyzer set to 0.01 second time constant

Rounding Off Test Data (Clause 0.4)

• Follow IS 2-1960 for rounding test results, matching significant figures of standard values

flowchart LR
    A[Fire Bell] --> B[Marking]
    B --> C[Manufacturer Name/Trademark]
    B --> D[Year of Manufacture]
    B --> E[Material Type]
    A --> F[Acoustic Testing]
    F --> G[Strike with Steel Ball (1 kg·m/s)]
    F --> H[Measure ≥ 100 dB at 5 m]
    F --> I[Frequency 600-1000 Hz]

This marking protocol supports traceability and standard compliance.