Inherently safer design (ISD) is a philosophy for designing and operating a safe process plant [1,2]. ISD aims to eliminate or significantly reduce hazards, rather than managing them with hardware and procedures. When feasible, ISD provides more robust and reliable risk management and, by eliminating costs associated with safety equipment and procedures, may make processes simpler and more economical.

ISD has received considerable attention from the public, government and non-governmental organizations (NGO) in recent years. Legislation to require consideration of ISD as an approach for reducing security concerns at chemical plants has been introduced in every session of the U.S. Congress since at least 2001, most recently as the Chemical & Water Security Act of 2009 (H.R. 2868), which was passed by the House of Representatives on November 6, 2009. The Senate will consider that bill this year (see "Anti-Terrorism Mandates Face Major Revision"). Also, New Jersey and Contra Costa County, Calif., require certain regulated hazardous-material-handling facilities to consider applicability of inherently safer technology (IST). Public interest, existing and potential regulations, and company and professional desires to design and operate safe facilities provide incentives for considering ISD/IST. But how do you actually do this for a real plant, either a new design or an existing facility?

The Center for Chemical Process Safety (New York City) recently released the second edition of its landmark book on ISD [3], first published in 1996. The new edition boasts a greatly extended discussion of how to actually implement ISD, including several examples and case histories. It also offers significantly upgraded checklists and other aids.

Levels of Inherent Safety
Over the years, considerable disagreement has arisen about whether or not a particular design feature of a process plant was "inherent" or not. Often the disagreement develops because people are looking at ISD from different perspectives. For example, from a high level viewpoint, an oil refinery can't achieve inherent safety because it must handle large amounts of highly hazardous materials. You can't avoid this in a refinery — the products are valuable because they contain a lot of energy. But that doesn't mean ISD doesn't apply. Used during detailed equipment configuration and design, it can eliminate or significantly reduce many risks within a process that still contains major hazards.