Some carbon blacks may contain compounds which are carcinogenic and as organic extracts of these have been classified as possibly carcinogenic to humans, special care should be taken to avoid exposure to such extracts. Lung effects remain controversial and may be due to contaminants. It is probable that minor effects reported are non-specific effects associated with exposure to nuisance dusts in general. Polyaromatic hydrocarbons (PAH) are reportedly present in some carbon blacks. Depending on the process of manufacture, there are variations in their chemical compositions. Carbon blacks containing over 8% volatiles may pose an explosion hazard (see Physical Dangers). Carbon black of mineral origin has no UN number and hazard classification. Card has been partly updated in October 2005. See sections Occupational Exposure Limits, Emergency Response.