Compressed Industrial and Medical Gases
Core concepts
Candidates must understand gas cylinders as pressure vessels: their test intervals, markings (test date, working pressure, tare weight, cylinder identification), and the requirement for periodic hydrostatic or ultrasonic examination. Know valve types - the pin-index valve system (medical) and the BS 341 / cylinder valve outlet standards (industrial) - and that pin-index systems prevent wrong-gas connection on medical cylinders. Understand colour coding conventions (e.g. oxygen white/black in many schemes, but always verify by label and marking rather than colour alone). Know oxygen hazards: oxygen is not flammable but intensely supports combustion, so oil and grease must never contact oxygen equipment. Know acetylene's special status - dissolved in acetone in a porous mass, never stored or used above about 15 psi (1 bar) gauge, and never on copper or silver fittings. Know argon, CO2, nitrogen and helium uses and hazards: nitrogen and argon are simple asphyxiants, CO2 is toxic at high concentration and heavier than air. Know medical gas pipeline systems: terminal units, zone valves, alarms, and the requirement for identity testing and purity verification.
Traps
A classic trap is treating oxygen as flammable - it is an oxidiser. Another is acetylene pressure limits and the ban on copper. Questions also test cylinder identification by markings rather than colour, and the difference between a simple asphyxiant and a toxic gas.
Worked rule of thumb
For a cylinder, usable gas content ≈ water capacity (L) × fill pressure (bar) for a rough estimate of free gas at atmospheric pressure; for example, a 10 L cylinder at 200 bar holds about 2000 L of free gas at 1 bar (idealised). Always confirm cylinder identity from the label and markings before connecting.