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How does a self contained breathing apparatus work?

3 min read

Asked by: David Cruz

The SCBA supplies the compressed oxygen from the oxygen cylinder to the wearer through cylinder valve, pressure reducer, demand valve, etc. Carbon dioxide in exhales air is absorbed by the absorbing canister, and oxygen is re-supplied through breathing bag. This mechanism enables for long time use.

How do you use self contained breathing apparatus?

In this method you hold the SCBA in front of you by the shoulder straps with the cylinder towards your body. Next grasp the cylinder with both hands and raise it over your head while working your arms through the loops of the shoulder straps and let the SCBA slide down your back. Next fasten and adjust the straps.

How long does a self contained breathing apparatus last?

The length of time that an SCBA tank will last depends on the user’s physical activity level. An SCBA cylinder capacity of 2,040 litres of compressed air gives the wearer approximately 51 minutes of air supply for full usage or approximately 30 minutes in working conditions.

What is an advantage of a self contained breathing apparatus?

Ease of mobility is a major advantage of the self contained tanks. The air from a SCBA is under positive pressure which is triggered by inhalation. The disadvantage of this method of respiratory protection is the level of training and proficiency required to become accustomed and agile with this equipment.

What is meaning of self contained breathing apparatus?

A self-contained breathing apparatus (SCBA) is a device worn to provide breathable air in environments with oxygen deficiency, smoke, dangerous gases, and other airborne contaminants that may be otherwise dangerous to breathe.

Who should be wearing self-contained breathing apparatus?


The Respiratory Protection standard specifically provides that firefighters entering an immediately dangerous to life or health (IDLH) atmosphere must wear a self-contained breathing apparatus (SCBA).

How do you don and doff self-contained breathing apparatus?

demonstrate the method of donning an SCBA while seated. Step 1: Position body in seat with back firmly against the SCBA and release the SCBA hold-down device. Step 2: Insert arms through shoulder straps. Step 3: Fasten chest strap, buckle waist strap, and adjust shoulder straps.

Why do firefighters carry compressed air?

Firefighters breathe compressed air, NOT oxygen when using their self-contained breathing apparatus. The cylinders are filled with air using a filter system to obtain the cleanest air possible. The mask has what is called a “demand valve” which only brings air into the mask during inhalation (breathing in).

Why are firefighter air tanks upside down?

SCBA bottles that firemen use are mounted upside down because they are generally smaller than scuba tanks and the risk of damaging the valve while running through a burning building in zero viz is much higher than the risk of damaging a scube valve while swimming (or scootering) through a wreck or cave.

What is the minimum period of time that the air supply for a self-contained breathing apparatus is required to last?

The duration of usage for breathing apparatus is between 10 minutes (short-term SCBA) up to about 45 minutes (long-term SCBA). Depending on requirements, you can use cylinder volume, pressure and thus the amount of compressed air specific to your application.

How is SCBA calculated?

The duration of the cylinder can be calculated with this formula: volume (in liters) × pressure (in bars) / 40 – 10 in minutes (the 10 is subtracted to provide a safety margin), so a 6-liter cylinder, of 300 bar, is 6 × 300 / 40 – 10 = 35 minutes working duration.

What are the important checks before using a breathing apparatus?

Ensure bypass v/v is fully closed. Open cylinder valve to check if cylinders are fully charged, whistle will be heard as the pressure rises. Demist mask visor with anti dim solution.