MAPP gas has a detectable odor at 100 ppm or at a concentration 1/340 of its lower explosive limit.

Small fuel-gas systems may leak 1 or 1 1/2 pounds of fuel or more in an S-hour shift; bulk systems leak even more. Fuel-gas leaks are often difficult to find and oftentimes go unnoticed; however, a MAPP-gas leak is easy to detect and can be repaired before it becomes dangerous.

MAPP toxicity is rated very slight, but high con- centrations (5,000 ppm) may have an anesthetic effect. Local eye or skin contact with MAPP-gas vapor causes no adverse effect. The LIQUID FUEL MAY CAUSE DANGEROUS FROSTLIKE BURNS because of the temperature at which MAPP gas must be stored.

OXYGEN.-Oxygen is a colorless, tasteless, and odorless gas slightly heavier than air. It is not flammable but supports combustion with other elements. In its free state, oxygen is one of the most common elements. Rusting of ferrous (containing iron) metals, discoloration of copper, and corrosion of aluminum are all due to the action of atmospheric oxygen. This action is called "oxidation."

When oxygen is supplied for use in oxyacetylene welding, oxygen is contained in seamless steel cylinders. A typical oxygen cylinder is shown in figure 3-52. Oxygen cylinders are made in several sizes; however, you will find the size most often used in welding and cutting is the 200-cubic-foot capacity cylinder. It is 9 1/8 inches in diameter and weighs about 145 pounds. This cylinder is charged to a pressure of 2,000 psi at a room temperature of 63F (17.2C).

You can tell the amount of oxygen in a compressed-gas cylinder by reading the volume scale on the high-pressure gauge attached to the regulator.

REGULATORS. - The gas pressure in a cylinder must be reduced to a suitable working pressure before it can be used. This pressure is reduced by a regulator or reducing valve. Regulators that control the flow of gas from the cylinder are either single stage or double stage. Single-stage regulators reduce the pressure of the gas in one step, while two-stage regulators perform the same work in two steps or stages. Generally, less adjustment is necessary when two-stage regulators are used.

Figure 3-53 shows two SINGLE-STAGE regulators: one for acetylene and one for oxygen. The

Figure 3-52. - Typical oxygen cylinder.

Figure 3-53. - Single-stage regulator.