Lead-based paint - The Federal definition is at least 1 milligram per square centimeter of lead on a surface or at least 0.5 percent by weight.

A lead-based paint hazard is a condition that causes exposure to lead sufficient to cause adverse human health effects. Lead hazards include:

• Deteriorated lead-based paint. As paint ages or is damaged, it deteriorates and may create hazardous conditions including lead-based paint chips, and lead-contaminated dust and soil.
  
  
• Friction, impact and chewable surfaces. Certain surfaces are subject to damage and, therefore, likely to generate lead-contaminated dust, soil, and paint chips. These include
  • surfaces subject to friction or abrasion such as stair tread and window sashes,
  • surfaces subject to repeated impacts such as door frames, and
  • surfaces that are available to children to mouth or chew such as window sills and door frames.
    
    
• Lead-contaminated dust. Lead-contaminated dust is dust with lead concentrations that exceed Federal standards. Lead-contaminated dust can come from lead-based paint that is deteriorated, disturbed, or subject to friction. It can also come from lead-contaminated soil. It is not always visible to the naked eye and it is difficult to clean up.
  
  
• Lead-contaminated bare soil. Lead-contaminated soil is bare soil around a residence that has lead concentrations exceeding Federal standards. Deteriorating exterior paint that contains lead and past emissions of lead gasoline are the primary sources of lead in soil. Lead-contaminated soil can be tracked into a home by people or pets and become dust that is ingested.