When you visit a work site, you’ll often see every construction worker wearing a hard hat. If they aren’t, then they’re violating Occupational Safety and Health Administration (OSHA) regulations. Employers in certain industries in the United States are required by law to provide all of their workers with a hard hat for their own protection.

Even though they’re required to provide them, employers often don’t or they’re the wrong ones. Data published by the Bureau of Labor Statistics in 2011 showed that 393 construction workers died that year after being struck by flying or falling equipment or objects at work sites. At least one of those could be attributed to them not wearing a hard hat.

If you’re wondering how effective a hard hat is in protecting you from injuries, that depends on its class and what you’re doing while wearing it. All are effective in protecting your eyes, head and neck, bumps, impacts and scrapes. Certain types can also prevent against electrocution.

OSHA’s ANSI Z89.1-1986 regulation spells out the difference between the two primary types of approved protective hard hats.

Type 1 hats are intended to keep the worker’s head safe if objects fall on it. They have a full brim that goes all the way around the dome of the helmet.

The interior of type 2 hats is outlined in foam which is expected to provide the worker with both lateral and vertical protection. Type 2 hats don’t have a brim that continues around the perimeter, but instead have a bill much like a baseball cap.

Hard hats are also arranged by class. General class G helmets aren’t just expected to protect the wearer from falling objects, but to also protect them against up to 2,200 volts worth of an electrical charge. Class E, or electrical ones, can withstand up to 20,000 volts. Class C, or conductive ones don’t provide a worker with any protection if they’re exposed to an electrical current.

While your employer is supposed to provide you with a helmet that is the correct type for the role that you’ll be performing, there’s no guarantee that they will — so workers might want to double-check that they’re using the right kind of hard hat. Workers who are hurt at a New York construction site may want to talk with an attorney about the ability to recover medical costs and lost wages.