nevătămător/lipsit de nocivitate
dar poate fi si iritabil (în cantintăţi mari) deci depinde de context
...considered to be in the category of a nuisance dust, i.e., a dust that is generally innocuous and not recognized as the cause of
serious pathological conditions.
http://www.cwc.org/plastic/pl977fs.pdf

aici nu e vorba de acidul boric dar explică bine la ce se referă 'nuisance dust'
http://www.syntechproducts.com/syntech4.ivnu
Nuisance dust or inert dust can be defined as dust that contains less than 1% quartz. Because of its low content of silicates, nuisance dust has a long history of having little adverse effect on the lungs. Any reaction that may occur from nuisance dust is potentially reversible. However, excessive concentrations of nuisance dust in the workplace may reduce visibility (e.g., iron oxide), may cause unpleasant deposits in eyes, cars, and nasal passages (e.g., portland cement dust), and may cause injury to the skin or mucous membranes by chemical or mechanical action.

Este folosit ca antiseptic deci nu e toxic
http://en.wikipedia.org/wiki/Boric_acid

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Note added at 1 day7 hrs (2010-04-10 17:28:04 GMT)
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În funcţie de criteriile de clasificare sunt mai multe tipuri
http://www.syntechproducts.com/syntech4.ivnu
Fibrogenic dust such as free crystalline silica (FCS) or asbestos, is biologically toxic and, if retained in the lungs, can form scar tissue and impair the lungs' ability to function properly.

Nuisance dust or inert dust can be defined as dust that contains less than 1% quartz. Because of its low content of silicates, nuisance dust has a long history of having little adverse effect on the lungs. Any reaction that may occur from nuisance dust is potentially reversible. However, excessive concentrations of nuisance dust in the workplace may reduce visibility (e.g., iron oxide), may cause unpleasant deposits in eyes, cars, and nasal passages (e.g., portland cement dust), and may cause injury to the skin or mucous membranes by chemical or mechanical action.

From an occupational health point of view, dust is classified by size into three primary categories:

Respirable dust
Inhalable dust
Total dust

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Note added at 1 day7 hrs (2010-04-10 17:33:54 GMT)
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se poate sublinia că, în cantităţi mai mari, este NEPLĂCUT/IRITABIL, etc.