Why can't you use PVC for gas line?

You don't need a plumber, you need to call Hank Hill.

Or you could use:

API 5L - Steel pipe

ASTM A53 - Steel pipe

ASTM D2513 - Thermoplastic pipe and tubing

When purchasing PE plastic pipe, the pipe must be marked ASTM D2513. Plastic pipe with this marking is the only PE pipe suitable for gas service.

Plastic pipe and tubing should be protected at all times from damage by crushing, piercing, or extended exposure to direct sunlight.

I'm building an outdoor BBQ island with a natural gas grill and side burners. My building inspector and I came up with a plan. I'm going to rough in the gas line and pressure test it and then I'll have a plumber tie it into the gas meter. But, part of the conversation didn't sit right with me. I asked him if I should just run the yellow HDPE gas line underground with a collar around it where it comes out of the concrete or if I should sleeve the whole run in PVC with the end by the house sealed so any leaking gas would escape at the BBQ island (I live in earthquake country and this is what was done when we remodeled our indoor kitchen).

He told me that both are acceptable and that it's up to me. I pushed him to give me his take on pain-in-the-butt vs. safety, but he wouldn't budge. He just told me that I could do this job either way.

Now, this is my house and I want it to be safe, but I don't like overdoing things for no real reason or that make a job more difficult (running the poly pipe through the PVC). I read that you can't smell a gas leak that comes up through the ground since the smell is absorbed by soil so the PVC sleeve system would run the gas away from my house, but is this worth the extra money and effort?