The objective of the work described in this paper was to develop the Hospital Emergency Support Function (HESF) model, which could be used by hospitals to augment medical surge capacity based on the reallocation of internal hospital personnel, in the wake of a catastrophic natural or manmade disaster. A group of subject matter experts, including clinicians with disaster response experience, hospital emergency coordinators and business continuity planners, was assembled to conceptualise the basic framework of the HESF model. The model was validated via feedback from a panel of decision makers at Yale-New Haven Hospital and development of a consensus among the panel, using a modified Delphi method. Hospital personnel and departments were reviewed, evaluated and stratified according to their latent contributions to medical surge capacity. Those pivotal to medical surge capacity were deemed HESFs, whereas those ancillary to medical surge capacity were considered non-critical or ancillary functions. Based on this classification, personnel assigned to non-critical hospital departments were identified as potentially divertible to HESFs, ie available to enhance medical surge capacity during a catastrophic emergency. The activation of the HESF model provides an alternative to utilising external resources for enhancing staffing during a medical surge event. The HESF model is based on the National Response Framework Emergency Support Functions and relies solely on internal hospital personnel to augment medical surge capacity in the event of a medical and public health crisis.