Gas safety roof gauging control hatch adapter

In a crude oil storage tank having a corrosive liquid stored therewithin to provide a liquid phase and a vapor phase, said storage tank having a roof and a bottom, and an inspection hatch attached to the roof;

• the improvement comprising:
• said hatch includes a floor spaced from a lid;
• a hollow conduit having one end mounted in fixed relationship respective to said hatch in a position wherein said conduit upwardly opens into the interior of said hatch;
• said conduit being of sufficient size to enable a liquid sampling apparatus to be moved therethrough;
• said conduit coupled to and downwardly depending from said hatch into the interior of the tank with the other end of the conduit opening below the liquid level which separates the vapor phase from the liquid phase;
• whereby the liquid contained within the tank covers the bottom of the conduit and thereby forms a liquid lock which prevents the vapor phase of the tank from communicating with the interior of the hatch, so that a person can extend a sampling apparatus from the hatch, through the interior of the hollow conduit, into the liquid phase of the tank and obtain a sample without communicating the interior of the hatch with the vapor phase of the tank.

A method of isolating the exterior of a corrosive liquid hydrocarbon containing tank from the vapor space contained therewithin so that the liquid phase of the tank is accessible to a person standing on the roof of the tank, comprising the steps of:

• (1) fixedly supporting a conduit from the roof of the tank and extending the conduit down into the interior of the tank, with the lower end of the conduit opening in close proximity of the bottom of the tank, and the upper end of the conduit coupled to the roof and opening into the ambient;
• (2) isolating the upper end of the conduit from ambient by the provision of a hatch means mounted to the tank roof with the upper end of the conduit opening into the hatch means;
• (3) filling the tank with a sufficient quantity of liquid to cover the lower end of the conduit, thereby providing a vapor phase within the tank which is isolated from ambient by a liquid lock formed at the lower marginal end of the conduit;
• (4) using the interior of the conduit to run apparatus from the hatch means into contact with the liquid contained within the tank, thereby enabling the tank to be sampled and gauged, while preventing the vapor phase of the tank from reaching a person who may be present at the hatch means.