Oxygen gas in cylinders is used by many people at work and sometimes at home. It is used; in welding, flame cutting and other similar processes; for helping people with breathing difficulties; in hyperbaric chambers as a medical treatment; in decompression chambers for people who work in compressed air or in deep-sea diving; for food preservation and packaging; in steelworks and chemical plants. Pure oxygen, at high pressure from a cylinder can react violently with common materials such as oil and grease. Other materials may catch fire spontaneously. Nearly all materials including textiles, rubber and even metals will burn vigorously in oxygen. Text labels on cylinder can be damaged or for some reason may be illegible; if the label cannot be reliably read the cylinder should not be used. Cylinder tags (full/in-use/empty) are often misused and misunderstood and are a relic from systems used for compressed gases found in industry (welding torches, etc). Relying upon the pressure gauge reading is the most effective method of determining how much gas is left in the cylinder improved cues are needed to signify to non-experts when cylinders are "empty" (like the empty cylinder warning light on your dashboard). For example, caution labels stating which valves need to be open. The regulator pressure gauge appears to be direct measure of gas available in the cylinder - however it can be isolated from the cylinder by closing the cylinder valve. If this occurs the gauge is only reading pressure trapped between the cylinder valve and the flow meter/regulator valve. Compressed gas pin indexing systems should not be overridden or defeated under any circumstances.