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Can you please check this extract? Thank you.

Various supplements/additions are added to oil derivatives (additives) in order to get desirable characteristics/properties. These are usually very poisonous and highly flammable matters/substances, so that their handling requires special precaution measures at work.
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This is how I interpret it:

Various additives are combined with oil derivatives in order to obtain desirable characteristics/properties/qualities. These are usually very poisonous and highly flammable substances, so that their handling requires special precautions.

Comments  
Thank you Mister Micawber.