Posted on 14th Apr 2019 @ 8:16 PM

Interspiro/Sari Head harness for full face masks: User Bulletin

Divator, Spiromatic and Sari Facemasks are alternatively equipped with two Head Harness of differing thickness. 

The original (AGA part number 336 100 631) grey, moulded rubber harness produced from 1979 onwards, is 2.75 mm thick, so that longevity and elasticity for comfort and motile security / face-fit is best attained for surface use and air diving.

This harness has been provided for all surface and diving applications of the mask and it remains suitable for all, excepting very deep and saturation diving applications, where light breathing gases are used, such as Heliox or tri-mix.

The reason for this is that; at high gas viscosity and density, the harmonics of the breathing valve MAY cause occasional fluttering and cause bounce between the mask and face – not injurious but irritating and distracting. Part of the reason this had not been noticed before 1983, was that the impact of vastly improved dynamics and work of breathing in the Divator MkII, compared to the Divator Mk1 (1968 to 1981); or, for that matter, any other commercial facemask; had not been fully evaluated in the field and saturation trials had been largely machine done with sinusoidal breathing waves – which of course do not always happen with real divers.

Therefore, from 1983, the thicker head harness was introduced, not to increase longevity, fit or comfort but to take care of this particular, vibration phenomenon in saturation diving.
From 2016, this harness (AGA/Interspiro part number: 460 190 457) has been available in black rubber only and it is 3.3 mm thick.

I am frequently asked about the use of harnesses for underwater and surface applications – hence this bulletin. It is apparent that some SCUBA and Surface demand divers tend to over - tighten head harnesses; a habit perhaps given of poor face-fit and weight, on some “Band masks” and other, full face masks; and this has led to breakage of attachment lugs (especially with Silicone rubber and TPE masks, which are all much less robust)

VERY IMPORTANT

When donning Full Face masks, the head harness should be tight but not so tight as to stretch the rubber strap by more than a tenth of its length. When adjusted properly, you should be able to easily insert a finger between the face seal and your face, the face seal returning to seal of the face afterwards.

It is important to adjust the straps of the Divator/Spiromatic/Sari as follows.

After donning the Mask, simultaneously draw tight the BOTTOM straps by the jaw line.
Then draw tight the temple straps to comfortable tightness.
The top strap usually required little or no significant tightening.

Failing to follow this procedure can result in mask movement during use, displacement of diving or chemical protective hoods and potential in-leakage of water or toxic chemicals – even when using positive pressure, or safety pressure masks.