Helmets have been used by humans since ancient times, but it wasn't until the last 100 years that they evolved from warfare-exclusive use into the universal symbol for work that we know today.
It all started in the early 20th century when protective caps began being used for worker protection during the Hoover Dam (1931) and Golden Gate Bridge (1933) construction projects. Hard hat use expanded to mining and shipyard operations shortly after. Since then, hard hats have become a staple for workplace safety and protection. OSHA now mandates that anyone in danger of an impact head injury, falling or flying objects, or electrical shock and burns, should be protected by a protective helmet (OSHA 2012).