Lean Thinking and the Swiss Cheese Model

This pandemic has introduced many new terms and concepts into the popular consciousness. We work to flatten the curve. Policies now state that some businesses and jobs as essential. We are aware of the dangers of asymptomatic transmission. The “Swiss cheese model” is one such term. For those of us concerned with delivering good process outcomes as well as broader organizational transformation, it’s worth coming to grips with.

What is the Swiss Cheese Model?

British psychologist James Reason coined the term to describe of how to deal with hazards of failures from complex systems with interacting human, technological and natural components. The idea is that because we can expect no single layer of protection to be perfect, we need multiple layers of prevention and checks.

Prof. Reason explains, “In an ideal world each defensive layer would be intact. In reality, however, they are more like slices of Swiss cheese, having many holes…. The presence of holes in any one ‘slice’ does not normally cause a bad outcome. Usually, this can happen only when the holes in many layers…line up…bringing hazards into damaging contact with victims.”

Each slice of cheese, or layer of protection, reduces the risk to some degree. When two slices of cheese are stacked, their holes may or may not align. Likewise, any a mistake might slip through two layers of checks. However, as the stack of cheese slices grows taller, their holes are less likely to line up. It logically follows that as we have more layers of protection to a process or system, the less change problems will get through containment.

Swiss Cheese and the Quality Pillar of Lean

Doing defective quality work is a common hazard at the process level. When we create a defect, at best it requires stopping to do rework. At worst, the defect goes undetected and its damage multiplies with time. The traditional way of inspecting quality into a process is like drilling a hole through a block of cheese. The final inspection is intended to be thorough enough to catch defects before the product is released to the customer.

In contrast, to relying mainly on final inspection, the Lean approach is to build quality in at each process. This does not eliminate final inspection but instead brings the responsibility for quality into the hands of each person and process step. Individual responsibility is paired with authority to stop work and call for help when people find abnormal conditions.

This is often expressed as jidoka, or the quality pillar of the Lean system. An important element of this is something called JKK or “own-process inspection.” In essence, it’s systematic way to build processes that allow people to accept only good quality, follow the steps that make good quality, and pass on only good quality to their customer. When individuals take ownership of these three layers of cheese, Lean operations deliver robust quality outcomes.

Swiss Cheese, Tier Meetings and Layered Audits

We can see Swiss cheese effects at the level of Lean management systems also. In Lean contexts, daily management is structured around a series of overlapping status reviews. These start with brief daily huddles at the team level (tier 1) and are mirrored at each organizational tier above it, at appropriate cadence. Tier 2 monitors outputs of tier 1 and is in turn monitored by tier 3. When an issue escapes through, or is escalated beyond any single layer of cheese, there are several layers to catch it.

Lean management systems link together practices such as strategy reviews, kamishibai audits, leader standard work routines and gemba walks together with the tier meetings. This creates a system of checks, feedback loops and multi-layer Swiss cheese-style safeguards.

The Swiss Cheese Lean Journey Roadmap?

Regardless of the challenge we are facing, it’s comforting to have a roadmap to follow. Has this been tried before? How have others survived similar crises? What are the dos and don’ts? Are there best practices?

With nearly thirty years of Western companies studying, adapting and practicing Lean management, we should have a few proven implementation models. And yet many organizations struggle or fail with one-size-fits-most approaches. In reaction, some argue “Lean is learning” and argue that extensive experimentation is the only way. This is slower. It often results in reinventing the wheel, rediscovering well-known shortcuts.

My view is that Lean success relies less on the thickness, number or sequencing of the slices. Lean success relies more on giving agency and authority to individuals and teams to layer and line up the holes. When everyone takes ownership over their own slice, the Swiss cheese model works.

Slice, Stack and Safeguard

The point of the Swiss cheese approach is that it’s better to proceed with multiple safeguards rather than to pin our hopes on any single one. As long as we follow the science, adopt best practices, and make data-driven decisions, the specific combination of experiments may not matter so much. As a general rule, it seems that the more complex the system we are trying to manage or problem we are trying to control, the more layers of Swiss cheese we need.

 

---