What is the standard for testing hydrogen levels at the sealing points of hydrocracking units using a hydrogen detector?

Due to the low density of hydrogen and the complex conditions at the site, it is difficult to determine whether a direct airtight seal is better; naturally, the lower the value measured on-site, the better, and it should not exceed 10 ppm

The alarm setpoints for most combustible gas detectors are set between 0 and 100% LEL, with increments of 1% LEL. Since standards use percentages of LEL to determine the level of danger, the typical alarm limits are 10% or 25% LEL; on many instruments, the setpoint is set at 20% LEL. However, at any time, once the reading exceeds 20% LEL, it indicates a potential risk of combustion or an abnormal condition. 20% LEL is the most conservative, or highest acceptable, alarm setting for monitoring flammable and explosive gases or mixtures; in an absolutely safe environment, the level should be 0% LEL. However, in the absence of monitoring, if gas leaks occur in large quantities or accumulate over time, it can lead to high concentrations of flammable gases in the air. Once these concentrations reach a certain level, they can cause explosions when exposed to an open flame. This threshold is commonly referred to as the Lower Explosive Limit (LEL). Different flammable gases have different LEL values; for example, the LEL for methane (natural gas) is 5% by volume in air. In other words, if the methane concentration in the air is below 5%, no explosion will occur upon exposure to an open flame or spark. But once the concentration reaches or exceeds 5%, such an atmosphere can explode when exposed to fire.