BG-4 Long Duration Closed
Circuit Breathing Apparatus

• Lightest - 4 hour BG-4 weighs <30 pounds and utilizes military proven materials
• Coolest - lowest breathing gas temperature for closed circuit breathing apparatus
• Easiest - simple design fittings allow much easier service and testing
• Safest - positive pressure protection and double-seal mask
• NIOSH/MSHA Approved - TC-13F-341, TC-13F-342, TC-13F-343 and TC-13F-344

The BG-4 features an operating period of 4 hours in accordance with NIOSH CFR 30 and EN-145. The positive pressure in the entire breathing circuit makes the BG-4 particularly suitable for long-term missions in a toxic environment.

Modern materials and technologies plus microelectronics make for a comparatively low weight. The ergonomically shaped carrying frame, in conjunction with the new comfort harness system, ensure very good wearing comfort. Breathing comfort is the result of a low resistance CO2 absorber and an integrated breathing air cooler. Designed for easy maintenance and service, the BG-4 can be rapidly cleaned, tested and prepared for re-use once the mission has been complete; saving time and money. The Monitron, which provides alarm, pressure and test information, provides reliable information on the status of the BG-4 during the mission.

The Monitron is automatically activated as soon as the cylinder valve is opened. The pressure reading at the display unit is clearly visible with the segmented display. The exact pressure value can also be read digitally. The digital display can be illuminated in the dark by pressing the back-light button. Following activation, Monitron automatically performs a set test and a battery check. By opening and closing the cylinder valve, the user can perform a high pressure leak test in less than 15 seconds.

During normal operation, the Monitron display flashes a green "go" light visible to the user. When the pressure is low, the display will flash a red "warning" light. The Monitron features a two-stage residual pressure alarm. The residual pressure alarm sounds for 30 seconds when about 700 psi cylinder oxygen pressure and again continuously at 145 psi.

A closed circuit SCBA, like the BG-4, operates on the principle of rebreathing the air inside the breathing circuit of the SCBA. By rebreathing the air, the duration of the SCBA can be significantly extended. When the cylinder valve (14) is opened, 100% oxygen flows from the cylinder (13), through the pressure reducer (15), to the minimum valve (8) and to the constant dosage (10) outlet to fill the breathing circuit. As the wearer inhales, the oxygen is drawn through the inhalation hose (11) and valve (2) and hose (3). The exhaled air, containing carbon dioxide, flows through the soda lime scrubber (5). The scrubber converts the carbon dioxide into water. This chemical reaction also generates heat in the process. The "scrubber" breathing air flows to the breathing bag (6) and past the ice cooler (9). The constant dosage outlet continually adds oxygen to breathing air to replenish the oxygen which is consumed by the wearer. The ice cooler and the constant dosage help to cool the warm breathing air from the scrubber. For peak demands of breathing air from strenuous work, the minimum valve opens and fills the breathing circuit with additional oxygen. Any excess breathing air in the circuit is expelled through the relief valve (7). The Monitron digital pressure gauge (17) gives the user the cylinder pressure and LED lights to indicate go or no go.

Functional Diagram

Mask Connecting Piece Exhalation Hose Filter Pad Soda Lime Cartridge Breathing Bag Relief Valve Minimum Valve Cooler Constant Dosage Inhalation Hose Drain Valve Cylinder Cylinder Valve Pressure Reducer Monitron Basic Unit Monitron Display Unit