The flame deflectors in the propane BBQ are rusted to bits. They sit an inch or two above the flames. For making new ones, I know to not use any galvanized or painted sheet metal. What kind of sheet metal would not be a potential health issue?
Best would be a cast iron/steel piece, it would last forever and do exactly same as next item.
Second best would be mild carbon steel, what we call black steel where I come from. It rusts like no tomorrow but it is cheap, sturdy and no surprises.
Stainless is a waste of money, heat over time will both make it brittle and leach mystery compounds like chromium into nearby surfaces.
Galvanized is ridiculous, as propane heat will melt the zinc and it will make a puddle.
Best performance is heat resistant high alloy steel with large portions of nickel, molybdenum and others. What we call "kettle steel" in my neck of the woods. But that is hard to work into shape, difficult to weld, heavy as bricks and thus expensive.
I decided to try a large diy stainless steel drip pan fashioned from upcycled BBQ carts, which are everywhere on CL, placed about 1/2" below the grill grates, and about 6" above the flames of the four burners. We've been using tinfoil this way this spring. The SS metal ought to remain cooler than deflectors 1" above the flames. While it doesn't eliminate the risk of fumes, the lower temp ought to reduce the risk. Could also use an old cookie/baking sheet designed for kitchen ovens, but don't have one to spare.
I would use mild steel if making a part , many grills are painted or powder coated prior to using these metals it is a good idea to cure them by running them through a heat cycle prior to using for food consumption. Prior to purchasing a pellet smoker I used propane with mild steel trays I made to hold a little water and wood chips. The trays did last a few years but rusted out so I folded up another set. It was an inexpensive way to distribute the heat and get some smoke flavor out of a propane grill.
Stainless steel would be best; places like Home Depot have an assortment of aftermarket grill parts. Non-magnetic stainless would be better, but magnetic stainless is good ( as in modern auto exhaust systems). Aluminum will disappear fairly fast. Galvanized and painted steel are no health risk.