MA is relatively benign for your skin if washed off pretty quickly. Except for eyes. Use some kind of protection. I've been using it for years for pool, spa, and other jobs around the house/property and even acid washed our pool three times, so I'm pretty experienced using it. AND every once in a while a splash comes to my face area which could hit eyes without protection. As far as my skin goes I'm pretty much a "delicate flower". I've splashed drops, even straight 32% to nearly every part of my skin, over the years. It stings a bit but has never caused any burns; just stinging. Just rinse it off pretty quickly.
I've been told that plasterers use it to clean their hands.
The fumes are another story. Very unpleasant.
I like to dilute it especially for the spa. Always add acid to water in the bucket if you are diluting. If you do it the other way you will have more potential splash out of bucket. Acid is much heavier than water. Undiluted it falls pretty quickly to the bottom of a water filled body of water. On a post, here on TFP, someone posted a link showing how undiluted MA behaves being dumped into a pool. They used some kind of dye in the MA. It "dove" down the side of the pool, to bottom, and then to drain, amazingly fast. Sure made an impression on me.
When directions call for "keeping dry" they really mean it. Moisture, somehow, always seems to find its way into sealed containers, usually ruining the substance and sometime creating gases that not only swell the container but are also dangerous to inhale. Even in dry conditions, with proper storage, some gases will be produced and leak out of the containers. That's why it is so important to keep certain chemicals stored away from each other. Always open container in well ventilated space and don't stand over the container while opening. I, once, opened a chlorine or bromine feeder, located at the pump station, in very cramped quarters, bending directly over the feeder. The gases hit me like a brick wall and virtually knocking the breath out of me. After I recovered enough to get up I called poison control. They told me to go stand in a hot shower until the hot water ran out, to help clear my lungs. It was really scary.
gg=alice