Propylene glycol is deemed “Generally Recognized As Safe” (GRAS) by the US Food and Drug Administration (FDA), when used as instructed in direct food ingredients and indirect food contact applications. This makes Star brite's Boiler System Antifreeze an ideal choice for consumers looking for a safer, environmentally friendlier solution, in case of overflows, leaks, and spills. Directions: Please follow your system manufacturer's directions for proper usage. This product is not a concentrate, but may require dilution with distilled or deionized water prior to use. Check percentage of propylene glycol antifreeze solution with a calibrated PG coolant/antifreeze refractometer.