Self-igniting, toxic: metal, wood shavings?

[Query]

I have never worried about the metal shavings (swarf) that occur when sharpening blades. Should I?

Random web pages warn of self igniting properties of metal or grind stone shavings (swarf), along with wood shavings, sawdust and wood finishes (like linseed oil, tung oil, etc. - often used on wood products like furniture & paddles exposed to water), and are claimed to be fire hazards.

Supposedly, because they have a large surface/volume ratio, (and the finishes dry through oxidation rather than evaporation), they can all get hot enough to spontaneously ignite. And rags soaked in the finishing oils can too, especially if wadded up or put in a pile or enclosed container (though some say they soak the rags in water, and put them in an enclosed metal container before discarding).

And all these things (swarf, wood shavings, sawdust, wood finishes) burn they can supposedly generate toxic fumes.

Grinding tools (like powered skate sharpeners) produce hot shavings which could add to the issue even without self ignition. In a home shop, they might hit sawdust.

When I use Pro-filer to sharpen (a hand tool) the shavings stick to the grindstone (and eventually clog it, and need to be removed). Could those shavings be an issue?

BTW, Pro-filer is too slow to easily modify rocker profiles, but I've considered using a hand grinder to try. But those shavings get hot too.

Is this all nonsense? If not nonsense, what do those who shape metal or wood, or finish wood, do to be safe?

[AlbaNY]

I wouldn't worry about it.  That said I did start a fire once while cleaning my messy room as a kid, so I know it can happen.  I was piling things into trash, keep, paper to organise, and so on.  I will never know exactly what happened, but it appeared that some candies from Japan in foil wrappers reacted with something in a pile and it did ignite.  There was a burnt hole in the carpet by my door for many years after that I covered with a throw rug.  It was lucky to be noticed right away, and I then understood the warning about not keeping solvent covered rags and such is a serious matter.

At the rink the shavings were collected by a vacuum, and I doubt they became hot enough to worry over.  I used bench grinders on various metals and stuff just playing around as a kid in our machine shop without any problems despite having open buckets of gasoline, kerosene, and oil etc plus oil soaked gravel and dirt as the floor with a wooden work bench.  (The smell of that place is a core memory!)  It did go up in flames causing hundreds of thousands of loss when my dad was welding in there and a spark flew wrong.  My dad did not do things the OSHA way, and boy do I have stories about my childhood working on a farm that often horrifies therapists.   

A ProFiler isn't going to heat up the shavings so much. 

[Query]

People who make their own wood paddles outside this forum have warned me that indeed boiled linseed and tung oil - often used to finish and sort of waterproof wood - ignite at fairly low temperature. In particular, that if you crumple up a rag (or paper towel) that has been soaked in those oils, oxidation can sometimes warm up the rag enough to ignite it. (Also, for much the same reason you shouldn't throw it in a trash container.)

I was told that the standard way to handle it is to soak the rag in water, and lay it out flat. That will slow down the oxidation enough that it won't get all that hot, and once it is sufficiently oxidized, the problem goes away.

(Also, someone who makes wooden paddles told me I shouldn't oil my paddle until it has had plenty of chance to dry out - maybe a few days?. Oiling a somewhat wet paddle would seal in the water, so it could rot from the inside.)

However, various people who work in shops have told me that metal filings, wood chips, and sawdust do not pose much of a fire hazard under ordinary conditions. However if the metal filings that come off of a grinding machine (and I guess this would include powered sharpening machines) hit sawdust or wood chips, they might be hot enough to start a fire in the sawdust or wood chips. So maybe it makes sense to vacuum up sawdust and wood chips before grinding or cutting metal in the same work area?

I wonder if throwing a lit cigarette on sawdust or wood chips could create a potential fire hazard too.

[AlbaNY]

I've known of barn fires that began from birds dropping lit cigarettes into hay chaff, so I'd expect sawdust to be a concern in that example. 

You are really overthinking this if you are worried, imo.