How Manufacturers Can Put Safety First with SIL Compliance

“Safety first” has become a colloquial joke of sorts that applies to all kinds of real-life situations, but it’s no joke when it comes to industrial control systems. Ensuring that products in these systems — such as emergency shutdown or automatic speed control — do what they’re supposed to when they’re supposed to can actually mean life or death in some situations.

Safety Integrity Level (SIL) compliance, a global standard for the safety level of control systems, is a key way machinery manufacturers can ensure customers and partners that their products’ control systems are in top working order, said Thomas Maier, principal engineer for functional safety at Underwriters Laboratories (UL). UL verifies, investigates, and tests that a certain control system actually complies with a certain SIL level. On Oct. 6, the group will host a free educational webinar on SIL compliance beneficial for design engineers (see link to the webinar below). Maier will be the speaker.

Maier, who has global responsibility for technical soundness and quality of UL’s functional safety services, said SIL compliance has broad ramifications that go beyond the factory floor or single products, making it an important standard to achieve across horizontal and vertical industries.

Thomas Maier, principal engineer for functional safety at Underwriters Laboratories, said Safety Integrity Level (SIL) compliance has broad ramifications that go beyond the factory floor or single products themselves.
(Source: Thomas Maier)

“It’s critical because it’s important for safety in general,” he said in an interview with Design News. “Public safety, safety in the workplace, [safety] in a transportation system. There is no doubt about this.”

It’s also important to achieve SIL compliance with products and machinery because it increasingly will become a global quality and safety standard that sends a message to customers and partners, he said.

“More and more industries and end product standards will adopt SIL,” Maier said. “For more and more industries, to be able to provide components that are SIL compliant will become important for component and equipment manufacturers.”

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SIL compliance — which is measured in accordance with the IEC 61508 standard developed in 1998 — has four levels, with Level 4 being for systems with the most dire consequences if safety is not complied with, and Level 1 being the lowest, Maier said.

For example, “you may find the highest level in nuclear power plants where if something goes wrong, many people can become seriously injured or die,” he said, while the lowest level would be for a system that if something goes wrong, someone might suffer pain but there are no long-term consequences.

There are several steps engineers and manufacturers must take on the way to achieving SIL compliance. First they must identify the risk associated with a control system, Maier said. Once that is identified, they must make that control system reliable and robust enough to meet the demands of that risk, he said.

Once these steps are achieved, the rest turns into following implementation requirements according to the IEC standard at the SIL appropriate for the system, which can be a predictable process even across different types of components, machines, or products, Maier said.

“Once you know what the safety function is (is it an emergency stop or speed control in a vehicle etc?), once you have defined this, then you know the implementation level is really always the same,” he said. “The function that you implement, [and] the requirements to implement the safety function are the same regardless of what industry you are in.”

Maier conceded that engineers and manufacturers may balk at achieving SIL because it’s something “perceived to be complex and challenging.” This is firstly because control systems themselves and their components, such as microelectronics and embedded software, are already complicated systems in and of themselves, he said.

Combine this with the requirements to achieve SIL compliance, and it can be a daunting task, Maier said

“The requirements that you find in the standard, they are quite complex, too,” he said. “This is a relatively big standard — it has altogether 700 pages. It’s a cookbook, if you will, on how to design safety-level control to get a good safety level.”

However, manufacturers and engineers should not let the number of requirements or complexity stand in their way of taking the time and analysis needed to achieve an SIL rating because of the confidence in safety it provides their customers, Maier said.

“If a product is SIL-rated, it has certain functions that have certain reliability and certain robustness,” he said. “This allows the manufacturer to say that this product has a SIL level. Then the end user, their customers, they may use that product, and if they integrate it properly in their system, then they can reduce the risks they have in their system or application.”

Maier and UL will host a free webcast “An Engineer’s Roadmap to SIL Compliance” on Tuesday, Oct. 6, describing the certification and discussing the steps engineers can take to achieve it.

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Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.

[image via Stuart Miles / FreeDigitalPhotos.net]