Supplied air respirators guide

What advantages do each of these systems offer? It all depends on the situation in which you will be using the system. Compressed air respirators allow total freedom of movement, but can provide only a limited volume of clean air, which restricts the amount of time for which they can be used. A hose system supplying pressurised air provides an unlimited amount of clean air to workers, but limits their range of movement. That makes them suitable for extensive maintenance or cleaning jobs taking place within a fixed area, especially if hazmat suits are being used, which can also be ventilated using the air supply system.

The legal requirements for using compressed air respirators as occupational safety equipment are defined by the EN 137 standard.

• A pressure meter (manometer) is required which can easily be read by the wearer
• An alarm system must be in place which is triggered if residual pressure reaches 55 +/- 5 bar
  EN 137-1 also contains regulations on industrial applications, while EN 137-2 provides additional requirements for firefighting purposes.

Compressed air tanks are available with filling pressures ranging from 200 to 300 bar. The compressed air tank must be made of steel, aluminium or carbon fibre reinforced polymers (CFRP). CFRP tanks weigh the least, which makes them most comfortable to wear. The compressed air tank is also fitted with a cut-off valve. This is connected to the pressure reducer of the compressed air respirator.
To ensure proper functionality, it is important that the pressure never falls below 2 bar, so that moisture and foreign objects cannot penetrate inside the tank. Compressed air devices must be regularly cleaned.

According to the EN 1089-3 standard, compressed air tanks must include a plainly visible tank code which provides information about the contents of the tank and any possible hazards. For example, a black and white colouring on the shoulder of the tank indicates that this is a compressed air tank. The colour coding applies only to the tank shoulder. There are no restrictions on the colour of the outer coat.
The label must contain information about:

• the composition of the gas mixture,
• risk and security profile,
• the UN code number and name of the gas,
• the name of the gas manufacturer, as well as their address and telephone number.

Depending on the type of compressed air respirator, it can be used for anywhere from around 10 minutes (short-term use) to 45 minutes (long-term use). Choose the right tank volume, pressure and volume of compressed air based on the conditions in which the system will be used. Another important factor influencing length of use is the individual user's air consumption.
For example, a compressed air tank with a volume of 3 litres (short-term use), a pressure of 200 bar and an air volume of around 600 litres contains enough air for about 15 minutes for a user who consumes air at a rate of 40 litres per minute.

Compressed-air hose units are not intended for portable use. They must be supplied with clean air from outside through a compressed-air supply hose, using either a permanently installed clean air line or clean air tanks.
There are three different types of hose unit systems:

• Including a regulating valve: These systems provide a continual air flow, which results in a high air-consumption level. Application: for stationary air supply.
• Including a normal-pressure lung demand valve: The clean air is only consumed during the inhalation cycle. Air consumption is low.
• Including an overpressure lung demand valve: These systems produce overpressure of up to 5 mbar inside the breathing connection (for example, inside a full-face mask), so that hazardous substances from the ambient air cannot enter the mask. Application: for example, in atmospheres containing acutely toxic substances.