High pressure release when opening gas cap on 1956 Thunderbird

[zuburg]

Probably nothing, but I want to make sure this is normal. I finally got my 1956 T-bird roadworthy after 5 plus years.

When I opened the gas cap to add fuel, a huge release of pressure blew out the fill tube. The tank is not original and it was nearly out of fuel.

Is this normal or do I need some kind of vented gas cap? I assume the cap that came with the car is invented?