After the events of September 11, 2001, Air Products and Chemicals Inc. (APCI) developed a Security Vulnerability Assessment (SVA) methodology, consistent with the Center for Chemical Process Safety (CCPS) guidelines. This methodology is designed for efficient and thorough evaluation of a large number of facilities, ranging from small industrial gas sites to large chemical plants. This methodology evaluates The potential consequences and attack scenarios at a facility and the attractiveness of the facility as a terrorist target. The team then provides recommendations for engineering and security improvements. Participation in early SVA development exercises with industry and governmental agencies made it clear that it is critical to have a team approach that includes process safety, security, and site operations functional expertise. This paper presents an overview of the APCI SVA methodology and summarizes major findings and lessons learned. Findings from an SVA provide multiple levels of protection for our assets and the public. The engineering and security solutions from the evaluation are intended to deter, detect, delay, and respond to an attacker. they include: 1. Inherently safer alternatives such as reducing inventory, designing fail-safe systems, and improving plant layout. 2. Enhanced physical security systems such as fences, access control, and monitored intrusion detection. (C) 2004 American Institute of Chemical Engineers.