Are there generic recommendations for setting up an oxygen/hydrogen torch assembly, for example, to fuse quartz tubes? Of particular interest are the locations of check valves, excess flow control valves, and flash arrestors.

Precautions applicable to oxy-acetylene torches are likely applicable here and are a good starting point. Recommendations for the hardware are best provided by the cylinder supplier, and all these parts can be purchased from their respective catalog. All three devices in the question should have UL listings, FM approvals, or some other nationally recognized testing laboratory (NRTL) listing, which should include limitations on effective placement of these devices on the fuel line. Inquire with the valve/arrester supplier/manufacturer to see the listing and go to the NRTL web site that describes the basis and limitations of the listing, particularly its use with hydrogen.