A family member is suing for custody of his children because their mother is a crack cocaine user. He is sure that she has smoked with the youngest child in her presence and in their house when he is away at work. He willingly took a drug test when the court ordered her to take one (Both hair and urine). His urine test was negative, but when the hair test came back he had trace amount of crack cocaine in his system (120). He was devastated. Can this come from the air conditioning ducts in the home? He has never smoked crack or done cocaine. What else could cause this?

If he lives in a home where there is crack and other cocaine, anyone living in that house will show trace amounts, the dust in the air, the counter, the place it is stored at.
A large percentage of money we have in our wallets all have trace amounts in it, since so much money is used in drug deals.

I found your question really interesting and really feel for your family member who has tested positive and is a non user. Possibly he could request a retest. I looked up this issue on the internet and found that it is getting more attention and it is recognised that there is a need for investigation into passive exposure because of situations such as yours. Also drug enforcement officers have tested positive due to passive exposure but then negative on a retest. The following is from ushealthtests/hairq&a.htm

Q: What are the issues of environmental contamination?

A: Studies on environmental contamination of hair have been limited. To date, cocaine has been the principal focus of these studies and cocaine seems to be the drug most attracted to hair. Cocaine, in its smokable form, can deposit on hair. As mentioned above, the crack smoker will not only ingest cocaine, but will add more cocaine to his/her hair by mere proximity to the smoke during use. Most individuals who do not use cocaine will also not be around smoked cocaine. If an individual lives with a cocaine user, he/she could conceivably be subject to cocaine exposure in the living environment. The cocaine residue left by the user could result in both a urine and hair drug test positive if accidentally ingested in significant quantity by a non-user. If the donor lives with or spends time with a cocaine smoker, it is possible that the non-user may have some cocaine smoke deposited in his/her hair. If external exposure is limited, the cocaine should wash out of hair using normal hygienic methods. If the exposure is more intense, normal hygiene may not be sufficient to remove all of it.

I wish your family member all the best and am glad he has you for support.