During the loading or unloading of a gasoline transport vehicle subject to this chapter, leakage from any component of the gasoline transport vehicle or the vapor collection or control systems shall not equal or exceed 20 percent of the lower explosive limit (LEL measured as propane) when measured at a distance of one inch with a combustible gas detector. There shall be no avoidable visible liquid leak from such components. Components of the transport vehicle or vapor collection or control systems include all piping, seals, hoses, connections, pressure-vacuum seals, and other possible leak sources. The combustible gas detector used for determining compliance with this standard shall have a minimum range of 0 - 100 percent of the LEL as propane, a probe with an internal diameter of 1/4 inch (0.625 cm), and a response time less than 8 seconds with sampling line and probe attached. The combustible gas detector must be properly calibrated prior to testing.