 The riot protection helmets are usually made to be able to easily fit a Gas mask, especially when tear gas is being used.There have been rare cases of riot protection helmets being worn to protect against objects blown by tornadoes or fierce storms for example in England in the 18 January 2007 gale.The simplest form is a hard shell with reinforced padding, and a chinstrap and a hinge-up (usually polycarbonate) visor, as in this image.