As Mike has said, a sample point label (shown at the following link http://www.xtralis.com/opencms/opencms/system/m... ) can be used to deter such painting. However, the key requirement is to ensure that the Air-sampling Smoke Detector has the best quality air-flow monitoring to detect if one or more holes has been blocked and raise a fault indication. The link below describes some of the issues in high airflow envionments http://www.xtralis.com/opencms/opencms/system/m...