QACs are used at concentrations ranging from 200 to 400 ppm for various food-contact surfaces. QACs are generally very stable, mostly unaffected by pH levels, and remain effective on a food-contact surface for a long time. Their antimicrobial activity is more selective than that of other disinfectants, they are inactivated by organic soil, and they should not be diluted in hard water. QACs are, however, generally very effective against bacterial biofilms. An example of a QAC is benzalkonium chloride, which is often used as a cleaner and sanitizer for various food surfaces, both at home and in industrial applications such as dairy equipment.