You don't want it to be completely sealed, because it will eventually warm up and boil. If it does so in a sealed container, PV=nRT implies that your container

You don't want it to be completely sealed, because it will eventually warm up and boil. If it does so in a sealed container, PV=nRT implies that your container will either need to expand dramatically or handle a lot of pressure. This can be....unexpectedly invigorating, especially if the container is strong. Instead, it's common to have a pressure-relief valve, often coupled with a gas sensor to make sure everything remains safe.