Method and apparatus for predicting the explosiveness of a volume containing inert gas and hydrocarbon vapors when mixed with air

A method of changing the inert gaseous content of a volume containing an inert gas mixture including hydrocarbon vapors to air without producing an explosive mixture of hydrocarbon vapors and air in said volume, comprising:

• obtaining a sample of inert gas including hydrocarbon vapors from a volume having an inert gaseous content including hydrocarbon vapors;
• mixing said sample with air to form a mixture;
• monitoring said mixture as it is being mixed for values including tenths of lower explosive limit and percentage of oxygen;
• providing a graph having the tenths of the lower explosive limit of the volume plotted along one edge of the graph and the percent oxygen of the volume along another edge of the graph;
• finding the point on the graph which corresponds with coordinates representing the values of tenths of lower explosive limit and percent oxygen of said volume;
• and
• adding inert gas to said volume for a period of time if the point is above the critical dilution line prior to ventilating said volume with air to remove the inert gas from said volume without producing an explosive mixture of hydrocarbon vapors and air.

A method of changing the inert gaseous content of a volume containing an inert gas mixture including hydrocarbon vapors to air without producing an explosive mixture of hydrocarbon vapors and air in said volume, comprising:

• obtaining a sample of inert gas including hydrocarbon vapors from a volume having an inert gaseous content including hydrocarbon vapors;
• mixing said sample with air to form a mixture;
• monitoring said mixture as it is being mixed for values including tenths of lower explosive limit and percentage of oxygen;
• providing a graph having the tenths of the lower explosive limit of the volume plotted along one edge of the graph and the percent oxygen of the volume along another edge of the graph;
• finding a first point on the graph which corresponds with coordinates representing the values of the tenths of lower explosive limit and percent oxygen of said volume;
• finding a second point on the graph representing 0.0 lower explosive limit and 21% oxygen;
• drawing a straight line through said first point and said second point;
• determining if said straight line crosses a vertical line representing the lower explosive limit of said volume;
• adding inert gas to said volume, and if said straight line intersects said vertical line prior to ventilating said volume with air to remove the inert gas from said volume without producing an explosive mixture of hydrocarbon vapors and air.

Apparatus for predicting the potential explosiveness of a gaseous volume containing inert gas and hydrocarbon vapors when air is added or substituted for said inert gas in said volume, comprising:

• means for obtaining a gaseous sample of said inert gas and hydrocarbon vapors;
• means for mixing said sample with air to form a resultant mixture thereof;
• means for measuring the fraction of the lower explosive limit of the hydrocarbon vapors in said resultant mixture, said lower explosive limit being the unit minimum quantity of hydrocarbon vapors in a gas needed to support combustion;
• means for separately measuring the percentage of oxygen in said resultant mixture;
• and
• means for summing said measurements of said fraction of the lower explosive limit and the percentage of oxygen, said sum being an indication of the explosiveness of said inert gas and hydrocarbon vapors when mixed with air.

Apparatus for predicting the explosiveness of a volume containing inert gas and hydrocarbon vapor when mixed with air, comprising:

• a sampling hose having one end locatable in a gaseous volume containing a mixture of inert gas and hydrocarbon vapors to which it is desirable to add air;
• at least a pair of valve means, one of said valve means being connectable to the other end of said sampling hose to regulate the flow of said gaseous mixture through said hose, the other valve means being connectable to a source of air to regulate the flow of oxygen therethrough;
• a tee having three innerjoined passages wherein the two passages are respectively connected to each of said pair of valve means;
• a catalytic combustion indicator having its inlet connected to the third passage of said tee so that a selectively combinable sample of said gaseous mixture and air may be regulated by said valves to flow to said indicator, said indicator including means to measure the fraction of the lower explosive limit and the percentage oxygen of the combined sample;
• and
• means for recording the sum of said measurements as an indication of the explosiveness of said volume containing said mixture of inert gas and hydrocarbon vapors if air were added to said volume.