Chevron refinery fire Chemical

Inherently Safer Design

The concept gains attention as chemical facility incidents continue to occur


Key components

The concept of ISD began with chemical safety expert Trevor Kletz. After a chemical explosion killed 28 workers in 1974 in Flixborough, England, Kletz focused on proactive steps that could prevent subsequent disasters.

Forty years later, Kletz’s mission endures with four key principles of ISD, as outlined by the Center for Chemical Process Safety:

  1. Substitute – If a less hazardous material is available, it should be considered.
  2. Minimize – Reduce the amount of hazardous materials whenever possible.
  3. Moderate – Cooler temperatures or lower pressures often can lead to less hazardous conditions.
  4. Simplify – By removing unnecessary complexity, processes become more user-friendly and less prone to failure.

As a basic-level example, Amyotte mentioned the shed in his back yard. Instead of storing gasoline for his lawn mower in a 45-gallon drum, he uses a 20-liter red plastic container. The strategy is inherently safer because he has minimized the inventory of hazardous material.

“That’s one of the basic, fundamental concepts of inherent safety,” Amyotte said. “I could have a 45-gallon drum of gasoline in my shed, and have physical barriers around it and develop safe work procedures and use PPE around it all the time. Or, I could just remove that hazard and just set the very small container there that’s inherently safer.”

No cure-all

Beyond the basics of ISD, plenty of obstacles exist.

What if eliminating one risk creates a different risk? What if certain ISD features are not economically feasible? How much, if at all, should ISD be government-regulated as opposed to voluntary?

“It’s a simple concept at its core,” Amyotte said. “It’s more complicated to implement.”

The complications vary. Take, for example, a plant that substitutes one material for another that is less hazardous, Crowl said.

“But maybe you need more of that material,” he said. “And that material all has to be brought in by truck. So, since you’re transporting more material by truck, you’re actually increasing the risk to the people who live around the routes in which those trucks are shipped.”

Meanwhile, the implementation of ISD does not eliminate the need for administrative controls and other safety strategies.

“Awareness is good, but I think people need to be aware of this concept. Workers and people that live around the community, they have to recognize that there are constraints to this,” Crowl said. “There are economic constraints, there are risk-shifting issues, and sometimes it’s not absolutely clear if indeed one option is more inherently safer than the other.”

Looking forward

As ISD continues to garner attention, many experts see progress. “I think we’re seeing a lot [of progress] in plants,” Hendershot said. “I think the biggest barrier probably is awareness and understanding of the potential, and I think another barrier is just a willingness to challenge the way things are.”

Often, people have approached Hendershot with different versions of the same question. The topic of inherent safety is interesting, they say – but how do you implement ISD?

“I think that establishing a goal is a large part of the solution,” Hendershot said. “Because what you really are talking about is being creative.”

The result of that creativity, combined with advances in technology and a greater awareness of ISD, could help to reduce the frequency of chemical fires, explosions and leaks. It is a continuing journey, Amyotte said, as more people look first to substitute, minimize, moderate, and simplify before turning to safety devices and other strategies.

“It will be very interesting to see where it goes, where we will be in the next five years,” Amyotte said. “Will the U.S. Chemical Safety Board still be writing investigation reports that keep saying, ‘Look, these inherent safety principles were not followed. Had they been, the incident might have been prevented’? Or will we get to the point where it’s being adopted more?”

Same idea, different field

How does the concept of Inherently Safer Design differ from that of Prevention through Design?

Not by much, according to experts. Both concepts have the same goal in mind, but ISD has been applied specifically to chemical plants and processes in hopes of reducing fires, explosions and toxic leaks.

“I would look at the distinction between process safety and occupational or personal safety,” said Paul Amyotte, a professor of chemical engineering at Dalhousie University in Canada. “Process safety is dealing with the prevention of fires and explosions and toxic releases – so, trying to keep energy and hazardous materials contained within vessels and within pipes. That’s the world in which inherent safety and Inherently Safer Design has been applied.”

As for the bigger picture, ISD and PtD each focus on pushing safety to the forefront. “In my opinion, it’s pretty much the same thing,” said Daniel Crowl, a professor of chemical engineering at Michigan Technological University in Houghton.

Dennis Hendershot agreed. He has written extensively about ISD as a process safety consultant with the New York-based Center for Chemical Process Safety of the American Institute of Chemical Engineers.

“It’s the same thing,” Hendershot said. “It’s the same thing in any field.

“The example I use when I teach it, it’s an ancient idea. Because if you had a family of cavemen living by a river and their cave got flooded out and they decided to move up the side of the hill, that’s an inherently safer design.”

NIOSH has long supported the PtD concept; however, it added a layer of controversy in recent months after the agency reversed course and withdrew its support of ISD in a letter to OSHA. The reversal stemmed from feedback that NIOSH heard from its stakeholders regarding possible unintended consequences, cost concerns and other issues, agency officials said. (For more on the controversy, see Washington Update, September 2014.)

Post a comment to this article

Safety+Health welcomes comments that promote respectful dialogue. Please stay on topic. Comments that contain personal attacks, profanity or abusive language – or those aggressively promoting products or services – will be removed. We reserve the right to determine which comments violate our comment policy. (Anonymous comments are welcome; merely skip the “name” field in the comment box. An email address is required but will not be included with your comment.)