A n-95 is better but a kn95 is better than nothing. Closing the vent or turning off the heat when he’s working is a good idea. Personally I would be more concerned with the regular dust particles than with any asbestos. It sounds like thats what gave your son a stuffy nose.

Even if there is a positive result on the asbestos test I still wouldn’t be very worried. There are guys who work with old drywall every day for decades and never develop any problems.

The negative health effects of inhaling asbestos appear 10-30 years after the exposure and it normally takes a lot of repeated exposures to be worrying. So it isn’t going to be asbestos that is giving your child a stuffy nose.

Its hard to tell from the markings/brand on the drywall alone if it contains asbestos. So the way to be sure is to take samples and have them tested. Its best to take at least 3 samples from different spots on the wall. It is also possible for there to be asbestos in the joint compound between the gypsum boards.

I would not be overly worried about the wallboard containing a large amount of asbestos though.

If getting samples tested is too expensive or inconvenient then you can try to minimize possible exposure. Use plastic sheets and tape to block off the construction area then cover anything inside it to prevent dust settling in. Tell husband to put the wallboard in trash bags and vacuum up afterwards. He should also be wearing at least an n-95 mask.