This thesis is an evaluation of an early intervention Employee Assistance Program (EAP) incorporating Critical Incident Stress Management (CISM) operating in the South Australian Ambulance Service (SAAS). The program was developed specifically for SAAS and is known as the Peer Support Program. The program was designed with the intention of mitigating the effects of cumulative and traumatic stress among SAAS personnel. It reflects the philosophy which has underpinned the concept of early intervention, which is to provide emotional first aid and identify individuals who have experienced traumatic stress in the course of performing their duties within the pre-hospital care environment. The program further aims to reduce psychological injuries through the combination of psycho-education incorporating practical coping skills, initial crisis intervention offered by in-house service providers, namely Peer Support Officers (PSOs) and, when needed, psychological intervention offered through referral to mental health professionals (MHPs). / For professional practice, the research shows that a CISM-based EAP is effective when used in its entirety, specifically pre-incident education, peer support selection and training, and confidentiality are key contributors to the success of CISM and CISM-based programs. Practitioners need to ensure that programs are appropriately developed and continually maintained. Researchers and practitioners must also acknowledge the emergency first aid philosophy underlying early intervention. In conclusion, the study demonstrated that a program developed with CISM guidelines can be effective in mitigating the effects of cumulative and traumatic stress among emergency service personnel in SAAS, thus disproving the claim that all such programs are ineffective and/or harmful. Furthermore, the study demonstrates the value of including qualitative evaluation techniques, and demonstrates that insightful data can be obtained through a multi-method approach. This undermines the argument that a quasi-experimental study is the only method suitable for evaluation and it is recommended that further EAP and CISM research focus on comprehensive, mulit-method evaluation. / Thesis (PhD)--University of South Australia, 2006.