A hazmat suit will protect you from radiation, which will protect you from a nuke anywhere on the map.

If you are standing directly next to the bomb itself, however, that 1cm of lead lining a plastic suit isn't gonna save you!

If you're within 700 hammer units of the nuke (which isn't actually very far, the ACS bubble is 200 hammer units, so it's about the radius of 2.5 ACS bubbles) then the physical explosion itself will deal up to 500 damage (scaled based on distance) to you in explosion damage, which is not the nuclear blast/radiation damage.

I'll discuss with the CM Team though and see if we should chalk this one up to common sense or change the description of the item.