I understand that a NIOSH mask is necessary if one is applying an oil-based polyurethane.

Is a NIOSH mask needed or advised if one is sanding a hardwood floor with a polyurethane of unknown type, but one that has dried many years ago?

On the (very possible) case that the polyurethane used was an oil-based one, will organic fumes be released again when sanding a perfectly dried such hardwood floor?


If an NIOSH-approved mask is recommended, Should I use an N95, N99, ... ?


1 Answer 1


NIOSH (National Institute Of Safety and Health) does not manufacture respirators or dust masks, they conduct research and make recommendations for prevention of worker injury/illness. If their name is on a respirator it means they approve of it's use for the manufacturer's stated purpose.

Generally. you should wear a particulate mask or respirator when sanding, mostly because of the chance for lead in old coatings. For old varnish the chance of significant lead exposure is slim and no volatile organics will be released.

However, you should wear a N99 dust mask or P100 particulate respirator anyway because breathing airborne dust when you don't have to is dumb. Ever blow your nose after working in a dusty field? Do you really want that stuff in your respiratory tract?

  • I wear a mask when sanding anyway. My question is: If I'm sanding hardwood because a few spots are worn out, does the respirator have to shield me from organic matter? Is it sufficient if it shields me from wood dust?
    – Calaf
    Apr 21, 2016 at 4:36
  • Once I saw the N, I wasn't careful about the two digits that follow. Now I see that there are multiple types.
    – Calaf
    Apr 21, 2016 at 4:44
  • I didn't mean to suggest you were dumb, good job wearing a dust mask. That should be sufficient, any toxic vapor is long gone unless you really heat it up, like with a heat gun or torch. The "95" and "99" refer to percentage of airborne particles filtered, so if the N99 is not significantly more expensive and is readily available, use it. An N95 would be OK too for sanding dust. The N99 are a bit less comfortable, generally, because they restrict airflow more and hold in moisture/heat from your breath more. Apr 21, 2016 at 5:07
  • No offense suspected. I was pointing out that you hadn't answered the question I was asking. Thanks for clarifying that the number refers to a simple measure rather than an elaborate specification. I do indeed dislike the fogging up of my glasses when wearing a mask, but maybe the ones with valves will solve this problem by releasing the air exhaled faster than a mask without a valve.
    – Calaf
    Apr 21, 2016 at 5:18
  • As a wearer of glasses, I can say that valved masks are way better. Even better is something like a 3m 6000 series half mask, which will give you flexibility to choose between particulate/OV/etc requirements. Apr 22, 2016 at 2:16

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