self contained breathing apparatus

A self contained breathing apparatus , or SCBA, sometimes referred to as a compressed air breathing apparatus, or simply breathing apparatus BA, is device worn by rescue workers, fire fighters and others to provide breathable air in an "immediately Dangerous to Life or Health" atmosphere IDLH. When not used underwater, they are sometimes called industrial breathing sets. The term "self contained" means that the breathing set is not dependent on a remote supply (e.g. through a long hose). If designed for use under water, it is called SCUBA (Self Contained Underwater Breathing Apparatus).

 

An SCBA typically has four main components.

 

1.    a high pressure tank

2,216 to 4,500 psi, about 150 to 300 atmospheres

2.    a pressure regulator

3.    an inhalation connection

·       Mouthpiece,

·        mouth mask or

·       face mask,

4.    Carrying frame.

A self contained breathing apparatus may fall into two different categories.

1.    open circuit

2.    closed circuit

Open circuit:

Open circuit filled with

·       filtered air

·       compressed air or

·       pure oxygen

Open circuit systems have two regulators,

1.    A first stage regulator to reduce the pressure of air to allow it to be carried to the mask.

2.     Second stage regulator to reduce it even further to a level just above standard atmospheric pressure.

This air is then fed to the mask via either

a demand valve (activation only on inhalation) or

a continuous positive pressure valve (providing constant airflow to the mask).

Open Circuit Rescue or Firefighting SCBA.

An open circuit rescue or firefighting SCBA has

·       a full-face mask

·       regulator

·       air cylinder

·       cylinder pressure gauge

·       harness

·       adjustable shoulder straps

·       waist belt

·       carrying Frame

The cylinder usually comes in one of three standard sizes:

1.    4 liter

2.    6 liter

    3.    6.8 liter

Formula for calculation of cylinder's duration:

Volume (in liter) x Pressure (in bar) /40 – 10 in minutes (the 10 is subtracted to provide a safety margin)

For example:

A 6 liters cylinder, of 300 bars, is

6 x 300 /40 – 10

=       1800/40 – 10

=       45- 10

=       35 minutes working duration

Note: the relative fitness and especially the level of exertion of the wearer, often results in variations of the actual usable time that the SCBA can provide air, often reducing the working time by 25% to 50%.

Cylinder:

Air cylinder made of

·       Aluminum

·       Steel

·       Composite construction (usually carbon fiber wrapped)

The composite cylinders are the lightest in weight and are therefore preferred by fire department.

The cylinder must be

·       Taken out of service after 15 years

·       Hydro statically tested every 5 years.

Empty air cylinders can refilled from

·       Larger tanks in a cascade storage system or

·       Air compressor

Full face mask:

·       The full face mask of breathing apparatus designed for use out of water.

·       The mask can have a big full face window, or small eye windows.

·       The mask might have a small orinasal breathing mask inside, reducing breathing dead space.

·       The mask can also incorporate a two-way radio communication.

Types of Use:

There are two major application areas for SCBA:

1.    Fire fighting

2.     Industrial

3.    Medical (now coming in to practice)

Fire fighting SCBA:

·       It is to be expensive because of flame resistance and light

·       Has ADSU (Automatic Distress Signal Unit)

·       If movement is not sensed for certain length of time, usually between 15 to 30 seconds.

·       Has PASS (Personal Alert Safety System)

· When the cylinder air is for only 15 minutes remain