With rebreathers becoming more and more common around the world I decided to do my first user course for the Hollis Explorer Rebreather. The Explorer is a Semi-Closed Rebreather which only uses a small cylinder of Nitrox (32-40% O2) instead of two cylinders; one diluent and one pure O2.
Training started in the classroom with unit assembly and dis-assembly going through each part and its function in the rebreather. I arrived fully prepared to take pages of notes and diagrams but it really wasn't required; the Explorer is such a simple and user-friendly unit, paired with a great Instructor made it easy to understand. When you first come face to face with a rebreather you can feel a bit apprehensive about making a mistake but the Explorer's automated predive checks and PADI Checklists ensure that you complete each step in the correct order. In a nice relaxed environment we were taught how to correctly assemble the unit, pack the CO2 scrubber and go through the predive checks, with useful tips to look out for. The Explorer does not require any tools to assemble and is very straight-forward with many parts being colour coded to aid assembly. Once the scrubber was packed and the unit was assembled we were shown the predive safety checks. When you turn the Explorer on you must complete the predive checks to ensure correct function of the unit, all of this is explained by your Instructor and the unit itself. The Explorer has a built in wrist computer which has a bright, colour coded screen that explains word for word what it is checking and any actions you need to take. It will start by calibrating the three O2 and optional CO2 sensors as these require calibrating every now and again just like your O2 analyser. After all of the checks the unit is ready to dive and will not allow you to progress unless each check is completed in the correct order.
After we assembled our Explorers and Bailout Cylinders we had a dive briefing on the skills expected on the dive and off we went. The Explorer feels different to Open Circuit SCUBA which I've been teaching for a few years now; in that there is no pressure behind the air that you breathe, the air that you breath is moved around the circuit by your breathing and one way valves. One of the best features of the Explorer is the complete absence of noise and exhalation bubbles around your face which allowed us to get up-close and personal with a few Pike, Roach and Perch around the Nautilus. The main difference, other than the breathing, is the change in buoyancy; with Open Circuit the volume of air as you breathe changes which changes your buoyancy and makes you sink or float. With rebreathers you have counterlungs which hold your breath either side of the scrubber so your gas volume only changes as you ascend and descend. All you need to do is alter your weighting and buoyancy in your BCD or drysuit and once you have done this you can hover effortlessly without having to concentrate on your breathing. You can hover motionless whilst breathing as heavy or as shallow as you like without ascending or descending which is perfect for performing tasks at a given depth. Skills required focused mainly on bailing out to Open Circuit but we also practiced no mask navigation and ascent, dSMB deployment, unresponsive diver underwater and others. Many of the skills are required to be performed whilst neutrally buoyant which is quite straight-forward when you've got your head around your buoyancy.