While my torch experience is Goldsmithing related, I concur with Doug Fattic. Check valves and flash arrestors are NEVER bi-directional! I agree with the configuration of having the flash arrestors at the regulator end of the torch hose and check valves at the torch end. Any “flash” arresting should be right before the fuel source rather than near the torch end. Hose failures or accidental cuts, along the hose, would negate the benefit of the flash arrestors. Ideally, the Propane tank will reside outside of the building and be supplied, via hose or rigid line, to the inside of the building and the torch. Most Fire Codes restrict Propane from being stored indoors due to its “heavier than air” properties. Propane gas detectors are available at RV suppliers/ dealers. Installing one or two in your workspace might not be a bad idea.
While it sounds improbable, 1lbs disposable bottles are legal to store indoors. For jewelry use, these little bottles have lasted for longer than a month. The POL tank fitting on the fuel regulator can be adapted to utilize these 1lbs tanks. There is something called a “reserve cylinder adapter” that will allow the disposable bottles to fit onto the regulator. These are designed to allow someone to finish cooking their steak on the grill with a 1lbs disposable bottle, when their 20lbs tank ran empty.
See:
https://www.amazon.com/GASPRO-Dispos...34169197&psc=1
Restrictions on storing propane gas indoors has been a major insurance and fire code issue for jewelry shops for years. This is how we manage the restrictions.
Good Luck!