Obviously, fireworks are the biggest safety hazard, which are illegal in Massachusetts.  And you've gotta wear lots of sunblock if you're outside all day.  But here are four hidden hazards to think about this weekend.

Dehydration.  Some of the early signs are dizziness, fatigue, and nausea.  So drink more water than normal.  And catch some shade every now and then.  Also, alcohol suppresses a hormone that helps you retain water.  And it stimulates your bladder and makes you pee more.

Ingredient-induced burns.  Also called phytophotodermatitis.  Lime juice on your hands reacts with sunlight and can cause bad blisters that won't show up for a day or two.  It can also happen with mangoes, carrots, and parsley.

Food poisoning.  Stuff that's refrigerated shouldn't be left out for more than two hours.  Or if it's over 90 degrees, just one hour.  Keeping stuff like raw meat in a cooler with ice is a good idea.  And also make sure nothing's too undercooked.

Heatstroke.  If you feel nauseous, have a headache, or get cramps, it's time to find some A/C, drink water, and maybe take a cold shower.  If you're confused, can't walk, or have trouble breathing, it's more serious.  Call 911, or go to the E.R.