An employee was introducing an air sparge to an atmospheric blending vessel which contained sodium glucoheptonate (SGH) mother liquid heated to approximately 210 degrees Fahrenheit. The employee opened a valve to introduce air at the base of the vessel and rise through the vessel contents. The valve was stuck and when the handle broke free it turned further than desired and released more air than intended. The air rising through the vessel caused the SGH mother liquid to splash out of a 23-inch diameter manhole in the top of the vessel approximately 11 feet above the employee. The heated liquid fell onto the employee causing first- and second-degree thermal burns to his back.