The window can be open to breath the ambient atmosphere with a great saving of gas.

A friction hinge permits the window to stop in the open position.

The mask body is of thermoplastic material strengthed with fiber glass to be indeformable for temperature variations and for aging. It is particularly guaranteed to impact strength and against water absorption.

To prevent brittleness problems the mask is made with a compact form with the application

of selectived materials.

The valve controls and the hand drive adjustments are natural and easy.

The neoprene hood with a Velcro fastening and earphones pockets is fitted onto the body mask by means of a steel strap.

The oro-nasal mask the molded face-seal of particular, anatomie form and the breathing valve features permit to wear the Full Face Mask M 400 for long time with comfort.

The M 400 FULL FACE MASK is the result of the efforts from G.S.D. to develop a diving mask

answering all the demands of professional deep diving and hard work with scuba equipment. In the past, particularly at the limit of air range 40/50 mt. and during the very deep oxyhelium dives (300 mt.) using commercial available demand valves, most of the divers found that the effort requifed by respiration was too high, causing frequently gasping which can cause loss consciousness.

The M 400 has been tested in a breathing simulator capable of simulating respiration at a frequency rate up to 60 cycles/min. and peak-flow up to 500 /t/min. (1.77 cu. ft/min.) in hyperbaric atmosphere.

Tests carried out at a diving simulator showed the need to develop a valve which wou/d give a resistance less than 25 cm. of water colum for inhale and exhale, and peak flow of 400 It/min. at 50 mt. of water depth using air or at 300 mt. using 1 % oxyhelium mixture.

Several commercial valves have been tested, none was capable of giving more than peak flow of 200 It/min., with a resistance below 25 cm. of water co/um in the inspiration and during expiration, the peak flow of the best valves did not exceed 150 It/min. for 25 cm. of vater column. Further tests, based on the amount of work done by the diver to breathe, have been done at the University of Zurich by the group directed by eng. Schenk.

These tests have demonstrated that the G.S.D. breathing-valve principle is the only one that will allow in the future to work, in safe conditions, at the depth required by the offshore programs. The design was to incorporate all the features suggested by the divers and to avoid defects found in the presently used mask.