Is a prison official liable under the Eighth Amendment for deliberate indifference to serious harm to an inmate?

"A prison official's 'deliberate indifference' to a substantial risk of serious harm to an inmate violates the Eighth Amendment." Farmer v. Brennan, 511 U.S. 825, 828 (1994). "[A] prison official cannot be found liable under the Eighth Amendment for denying an inmate humane conditions of confinement unless the official knows of and disregards an excessive risk to inmate health or safety; the official must both be aware of facts from which the inference could be drawn that a substantial risk of serious harm exists, and he must also draw the inference." Id. at 837.