Hydraulic fluid and fire-resistant fluid compositions and methods of using the compositions are provided. In an embodiment, the present invention provides a method of utilizing fire-resistant fluid in hydraulic systems. For example, the method can comprise utilizing fire-resistant fluid in hydraulic systems of casters found in steel mills, in an environment where fire safety is of concern. The fire-resistant composition can comprise one or more glycerin by-products derived from a biodiesel manufacturing process. The fire-resistant composition can also comprise one or more glycerin by-products of transesterification reactions involving triglycerides. The fire-resistant fluid can be added to hydraulic systems as a solution.