At approximately what pressure does the alarm bell operate on a pressure demand apparatus?

• A. 10-15%
• B. 20-25%
• C. 30-35%
• D. 40-45%

Answer: (B)

The alarm bell on a pressure demand apparatus typically operates at a pressure range of 20-25%. This pressure range is critical as it serves as a safety mechanism to alert users when the pressure drops below the minimum required for safe operation. In pressure demand systems, maintaining a specific pressure is essential for ensuring that the apparatus is functioning effectively and that the necessary air supply is adequate for the user's needs.

When the pressure falls into this 20-25% range, it indicates a significant enough drop that could compromise the integrity and functionality of the apparatus, thus prompting the alarm to alert the user to take action. This helps prevent situations where the user's respiratory needs are not being met, ensuring both safety and compliance with health and safety regulations in mining operations.

Other pressure ranges listed do not align with the standard operational parameters for alarm systems in pressure demand apparatus, thus making them less relevant in this context.