Back to Documentation List

Breathing Air Supply Calculator Documentation

Note: This documentation is based on standard safety calculations for Self-Contained Breathing Apparatus (SCBA). The actual implementation in the code may vary.

1. Objective

The Breathing Air Supply Calculator is a safety tool used to estimate the service duration of a breathing air cylinder (like an SCBA). It helps personnel understand how long their air supply will last based on cylinder specifications and user breathing rate.

2. Design Basis & Methodology

The calculation is based on the volume of breathable air available in the cylinder and the rate at which it is consumed.

Key Formulas:

  • Volume of Air at Atmospheric Pressure:
    V_air = (P_cylinder * V_water) / P_atm
  • Service Duration:
    Duration = (V_air - V_reserve) / Breathing_Rate

Where:

  • V_air: Total volume of breathable air.
  • P_cylinder: Pressure of the compressed air in the cylinder.
  • V_water: The water volume (internal capacity) of the cylinder.
  • V_reserve: A safety reserve volume (e.g., 25% of total air).
  • Breathing_Rate: The user's respiratory rate, often assumed at a standard value for moderate or heavy work (e.g., 40 Liters/min).

3. Input Parameters

  • Cylinder Water Volume: The internal volume of the cylinder (e.g., 6.8 Liters).
  • Cylinder Pressure: The starting pressure of the cylinder (e.g., 300 bar).
  • Breathing Rate: The estimated air consumption rate of the user.
  • Safety Reserve: The percentage of air to be held in reserve.

4. Output Results

  • Total Air Volume: The total volume of breathable air in the cylinder.
  • Available Air Volume: The volume of air available for use (Total - Reserve).
  • Estimated Service Duration: The calculated time in minutes until the reserve level is reached.

5. Limitations and Assumptions

  • The user's actual breathing rate can vary significantly based on exertion, stress, and physical condition. The standard rate is an estimate.
  • Assumes ideal gas behavior.
  • Does not account for temperature effects on pressure.

6. Example Calculation

Goal: Estimate the service time for a standard SCBA cylinder.

Given:

  • Cylinder Water Volume (V_water): 6.8 Liters
  • Cylinder Pressure (P_cylinder): 300 bar
  • Breathing Rate: 40 Liters/min (heavy work)
  • Safety Reserve: 25%
  • Atmospheric Pressure (P_atm): 1 bar (assumed)

Calculation Steps:

  1. Calculate Total Air Volume at Atmospheric Pressure: V_air = (P_cylinder * V_water) / P_atm = (300 bar * 6.8 L) / 1 bar = 2040 Liters

  2. Calculate Reserve and Available Air: V_reserve = V_air * 25% = 2040 L * 0.25 = 510 Liters V_available = V_air - V_reserve = 2040 L - 510 L = 1530 Liters

  3. Calculate Estimated Service Duration: Duration = V_available / Breathing_Rate = 1530 L / 40 L/min = 38.25 minutes

Result: The cylinder will provide approximately 38 minutes of breathable air before reaching the safety reserve.

Reference Standards

  • OSHA 1910.134: Respiratory Protection standard.
  • EN 12021: Respiratory protective devices - Compressed gases for breathing apparatus.
  • CGA G-7.1: Commodity Specification for Air - Grade D breathing air parameters.
Go to the Breathing Air Supply Calculator