Methods and systems for measuring the concentration of a light gas in a main flow stream are disclosed herein. The methods include calculating a control parameter as a function of the concentration of the light gas in the main flow stream; dividing a portion of the main flow stream to produce a feed stream; and separating the feed stream by selective permeation across a semi-permeable membrane to produce a permeate stream enriched in the light gas and a retentate depleted in the light gas. A ratio of the flow rate of the feed stream to the flow rate of the main flow stream may be increased or decreased according to the control parameter. In addition, an area of the semi-permeable membrane may be increased or decreased according to the control parameter.

A combustible gas that enables reducing an amount of CO.sub.2 generated at a time of cutting an object is provided. A combustible gas for use as a combustion gas for gas cutting of an object contains ethylene at a concentration of greater than 0% by volume and less than 18% by volume, with the remainder being hydrogen and unavoidable impurities. The combustible gas is preferably encapsulated in a container, and a pressure in the container at 35 C. is preferably 1 MPa or more and 50 MPa or less. A concentration of the unavoidable impurities is preferably 1.0% by volume or less. The object is preferably steel.

A system and method for automated blending of hydrogen gas with traditional fuels, such as natural gas, to produce a consistent stream of precision-blended flow with a single customizable, movable and modular unit that is automatically controlled, is disclosed. The system and method includes a self-contained modular unit, automatic flow control computers and systems, which are configured to automatically adjust the hydrogen blend for variable flow and pressures present in an existing distribution system, varying hydrogen and natural gas flow rates to maintain a repeatable percentage of hydrogen without manual operation.