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I've got 3M Power Tool Respirator (product page). It has a sander tool icon on the cover yet it reads "Do not use for hardwoods". From the wikipedia it seems as hardwood refers to all kinds of trees except conifers.

Did I understand this right? Doesn't this mask gets quite useless if this can be used only on conifers? I am about to sand some older wood pieces that might be hardwood.

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    "hardwoods" is a bit of a misnomer ... by definition, it's deciduous(hardwood) and conifer(softwood) trees. Typically hardwoods are more dense, but this isn't always the case. That's a pretty vague warning, I think. – Daniel B. Apr 9 '15 at 19:40
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The fact that there is any warning at all probably has to do with the fact that the mask's rating is only FFP2 and it can only filter 94% of dust particles, whereas other masks can filter 99% or more. FFP2 also only requires <8% inward leakage, which seems like quite a significant amount of leakage.

The reason the warning specifically mentions hardwoods may have to do with the fact that hardwoods are generally more toxic, as Daniel B. commented. A collection of points from a University of Illinois at Chicago paper state:

  • Contact with the dust of many hardwoods can cause conjunctivitis (eye inflammation), hay fever, asthma, coughing, and other respiratory diseases.
  • Some hardwoods can cause hypersensitivity pneumonia (alveolitis), and frequent attacks can cause permanent lung scarring (fibrosis).
  • Some hardwoods contain chemicals that are toxic.
  • Inhalation of hardwood dust is associated with a particular type of nasal and nasal sinus cancer (adenocarcinoma). This type of cancer has a latency period of 40-45 years, and occurs to the extent of about 7 in 10,000 among woodworkers who are heavily exposed. This rate is many times higher than the rate of nasal adenocarcinoma in the general population. Over half of all known cases of this type of cancer are found in woodworkers.

Yet the paper considers softwoods much less hazardous:

Softwoods do not cause as high a frequency of skin and respiratory problems as do hardwoods. A few individuals can develop allergic reactions to some softwoods.

Regardless of the higher rate of toxicity among hardwoods, any fine dust is hazardous and can cause respiratory ailments in sufficient quantities.

Keep in mind that most disposable masks cannot create as good a seal with your face as reusable respirators with replaceable P100 (or equivalent) filters, which filter 99.97% of particles 0.3 microns or larger.

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    Perhaps it's because hardwoods tend to be more toxic? – Daniel B. Apr 9 '15 at 19:43
  • @Daniel B. thanks, I incorporated that into my answer. – rob Apr 9 '15 at 20:05
  • @rob, thanks for the detailed answer, appreciated. – Alex Tereshenkov Apr 11 '15 at 6:39
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Masks rated for less than P100 are not recommended for hardwoods since hardwoods produce smaller, finer dust particles than softwoods. As each tooth cuts the wood, the depth of cut for a hardwood is necessarily smaller (otherwise you overload your motor) and the smaller depth of cut produces fine dust that can pass filters designed only for larger particles.

The problem is the same whether sanding, cutting, or performing man other wood operations with hardwood - finer dust is more likely with hardwoods than softwoods.

The filter you link to is better suited for construction use where most materials are soft and easy to cut, producing the much larger particles this product is intended to filter and less finer particles it isn't intended to handle.

  • Don't confuse hardwood (the classification) with hard (as measured on the Janka scale) wood. Also it is not true that the depth of cut is necessarily smaller on hard (Janka scale) woods because you could use a thin-kerf blade or your saw's motor may be perfectly adequate for the types of cuts you need to make. – rob Apr 10 '15 at 18:54
  • In my answer I originally speculated that hardwood might fragment into smaller particles as it is cut, but I've never really paid close attention myself and couldn't find any evidence to support this with a quick search. If you can find some supporting evidence and include a link, that would be great. – rob Apr 10 '15 at 18:57

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