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Chemical compounds possess several hazards. When working with chemical always look for substitution for a safer compound, read the label carefully and consult the safety data sheet.
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Activities with biological material are separated in 4 class, related to the hazard of the strain manipulated, the scale of the activity, the steps, etc.
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Most lasers can cause eye and skin injuries to anyone who is exposed to the direct beam or its reflections.
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Material whose 50% (at least) particles have one or more dimensions within 1 to 100 nm in size. Nanomaterials can be more harmful than their bulk counterpart.