A bump cap is a type of safety PPE that provides protection for your head.
They are designed to protect you from minor head bumps and lacerations. Bump caps are worn when there is a risk of impact between your head and stationary objects such as low ceilings, and overhead piping.
Bump caps are not designed to protect your head from falling or flying objects, like a hard hat would. When there is a risk of impact with moving objects, you must use a hard hat.
When compared to hard hats, bump caps are more lightweight, generally a bit cheaper to purchase, and are easier to wear. They do not impair your vision or add height to your head.
Although bump caps are a form of personal protective equipment (PPE), they are not used for situations in which an employer is obligated to provide his/her employees with head protection for the purpose of avoiding serious injury. They are only used to provide head protection in low-risk situations to reduce exposure to lacerations, abrasions, and minor bumps to your head.
Bump caps are not appropriate for any situation in which the use of ANSI-standards-compliant head protection is required.
Remember, a bump cap is only used to protect you against contact with stationary objects, whereas a standards-compliant hard hat or other piece of recognized head-protective equipment provides protection against more significant hazards, such as the impact of a falling object that could otherwise result in a fatal injury.