Gas Analysis for the Recreational and Technical Diver Joel D. Silverstein R.W. Bill Hamilton, PhD

OVERVIEW This workshop is an introduction to preparing oxygen enriched air. A Blending Technician should be certified to dive with the gas they intend to prepare. An Oxygen Service Technician should be certified by the manufacture to repair the scuba equipment they intend to convert to oxygen service. Initialy work with another technican until you feel comfortable working on your own.

EQUIPMENT LABELS Install a tank decal or wrap to identify the particular gas mixture; nitrox, trimix or O2. Install a contents-tag identifying the FO2 MOD, analysis date, fill pressure, and the analyzers/users initials. Use appropriate labeling for dedicated scuba regulators and gauges.

Identifying Enriched Air Cylinders 4 inch green band on yellow tank NITROX or Enriched Air stenciled in 2 inch high letters Non-yellow cylinders have an additional 1 inch yellow band above and below the green

Other identification labels Oxygen Service label designates cleanliness annually or if contaminated Visual Inspection annually or sooner Cylinder Contents identifies contents

ENRICHED-AIR SYSTEMS GAVIMETRIC METHOD Gavimetric mixing requires a sensitive scale that displays weight in 1/4 ounce increments up to 150 lbs. Eliminates mix variability from temperature and compressibility factors. Must know the volume of gas at ambient pressure for service rating of the cylinder. Scale and setup is expensive.

O2 ANALYSIS Analyze the cylinder contents before discharging it to the customer. Calibrate an analyzer to 100% O2 when the unit is new or the fuel cell is weak. Before analyzing gas, let the sensor equilibrate to ambient temperature and calibrate to dry air. Adjust flow rate to specifications and do not block the exit side of the flow tube.

Performing Gas Analysis overview Oxygen analyzers The need for calibration Need two analyzers ? Acceptable range Analyzing Gas Flow rate Calibration Analyzing the enriched air cylinder

Oxygen Analyzers Digital Analog 0.1% accuracy is desirable Electrochemical oxygen sensor has limited life span

The Need for Calibration Some units need a flow meter to be accurate Sets analyzer at a known value (air) Allows for adjustment of sensor deterioration Affected by flow rate Better to calibrate one well than to use two Air calibrates at 20.9% Calibrate on 100% when readings fluctuate

Analyzing the Gas Flow Rate Acceptable range affects reading the greater the pressure against the sensor the higher the value shown 1-2 Lpm for one minute calibrated at same flow Acceptable range desired mix +/- 1%

The Nitrox Cylinder Calibrate analyzer Analyze cylinder some auto calibrate Analyze cylinder Check for accuracy If not right recalibrate have gas re-mixed Write information contents label or tag

Contents Label and Fill Log Write on label Use permanent marker Fill date Oxygen % PSI (pressure) MOD Filled by Analyzed by User’s name Name Certification number Date Fill pressure Oxygen percentage Maximum depth limit Cylinder serial number Signature