What is the best practice for using spark resistant tools when working on systems containing hydrogen?

Because a small spark can ignite hydrogen-air mixtures, precautions such as using spark-resistant tools is one method that can be considered to reduce the probability of an ignition. However, there is little evidence that spark-resistant tools make a significant difference.   

Spark-resistant tools are made of nonferrous materials that are inherently weaker than the steels used for most tools. Therefore, these tools are heavier and more prone to being damaged while in use, which presents a different kind of safety hazard. The use of spark-resistant tools should be considered depending on the specific task to be performed.
It's important to note that the use of non-sparking tools does not allow work to be done in an area where a potentially flammable atmosphere may exist. They should not be used as a false sense of security for a person to work in an unsafe environment. Where possible, all systems should be properly purged and isolated from the hydrogen source prior to the start of work. In addition, the area should be ventilated and verified safe with a portable monitor. ISO 15916 - Basic considerations for the safety of hydrogen systems States that: “the use of spark free tools is not an absolute guarantee that no spark will occur. Even these tools might convey enough energy to a material or a material combination to create a hot spot or to rip off a burning particle. Personnel should ground themselves before touching or using a tool on a hydrogen system if any hydrogen is or is suspected to be in the area.”