With the Bulletproof Design of the Hollis HP5 Non-Balanced Flow-By Piston First Stage the HO2 First Stage is Certified for up to 100% Oxygen Service thanks to Highly Specialized Component Materials and Manufacturing Processes. Cleaned and Assembled in a Clean Room Environment with Specially Designed Materials, Halocarbon Based Lubricants and Color- Coded for Easy Identification The Flow-By Piston Design is the only true Fail-Safe First Stage Design on the market. The Piston will automatically move Downstream from the High Pressure Air coming from the Scuba Cylinder if there is an unexpected malfunction of the High-Pressure Seat. This feature guarantees a constant Gas-Flow to the Second-Stage Regulator. The Regulator First Stage weighs 8.3 oz (235.3 g).