Even a low-speed fall on a bicycle path can scramble your brains. Laws in 17 states and over 70 localities require helmets. Make sure your helmet fits to get all the protection you are paying for. A good fit means level on your head, touching all around, comfortably snug but not tight. The helmet should not move more than about an inch in any direction, and must not pull off no matter how hard you try.
Standards are no longer a big issue.
Look for a CPSC sticker. Pick a bright color for visibility to be sure that motorists and other cyclists can see you. Experienced, careful bicycle riders crash after 4,500 miles on the average. Nobody expects to fall, but in time you will too. When you do you must have head protection, since head injury causes 75 per cent of our 800 annual deaths from bicycle crashes.