Free Available Chlorine (FAC)
measurementThe portion of chlorine in a solution that is not bound to organic matter and is available to inactivate microorganisms.
Definition
Free available chlorine (FAC) is the sum of chlorine species — primarily hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻) — that remain unreacted and are available for disinfection. It is distinct from combined chlorine (chlorine bound to nitrogen-containing compounds such as chloramines) and total chlorine, which is the sum of both.
Why it matters
FAC is the practical indicator of disinfecting capacity. Regulatory limits, cleaning protocols and disinfectant labelling are typically expressed as parts per million (ppm) of free available chlorine because it directly correlates with microbial kill performance.
Practical applications
Measured with test strips, colorimetric kits or electronic meters in healthcare cleaning programmes, food-contact sanitising, swimming pools, cooling towers and drinking water treatment to verify that working solutions meet target concentrations.
Need help applying this?
Our team can help design the right disinfection protocol for your operation.