https://www.ffam.org/leather-fire-helmets/
https://my.firefighternation.com/group/firefightinghistorymyths/forum/topics/889755:Topic:233835
http://sfmuseum.org/hist/helmet.html
https://www.earlyusfirecos.com/equipmentmanufacturer/cairns-bros
And many scraps of information sourced from ebay pictures, facebook posts, etc.