Lessons from Science – Rate Limiting Step

Screen Shot 2013-06-03 at 9.12.17 PMI think most of us can grasp the idea of a bottle neck pretty easily. It’s the narrowest part of a bottle, and will limit how quickly you can pour your wine.

The term also gets used in business, where the step in a process or project that has a rate slow enough to be determining the completion time of the entire process or project.

A similar concept exists in chemistry, where one reaction in a series of reactions occurs at a slow enough pace that it determines the overall speed of the chain of reaction, it is called the rate-limiting step. I learnt about it in biochemistry 101, where metabolic pathways such as the break down of ethanol have an intermediate rate limiting step, the formation of Acetaldehyde which occurs quickly, followed by a slower breakdown of Acetaldehyde to acetate. It’s the build-up of Acetaldehyde that causes the physiological effects we associate with alcohol. Which also explains why if you drink slowly enough you won’t ever get drunk, whereas if you drink quickly the effects are soon felt. It was worth going to university just to learn that.

In a chemical process you get a buildup of whatever precedes the rate-limiting step, and you can occasionally increase the reaction speed by increasing temperature or adding a catalyst.

Similarly in a business process the slowest step determines the overall speed of the process, and if there’s a change in one step of the process the overall speed of delivery can be affected. And if a bottleneck is not analysed in a business process there will be consequences; much like the person who drinks too much too quickly. Usually the service or product to be delivered will be delayed or the quality reduced.

If you want to speed up a  business process analyse each step and look for the rate limiting step, assess the real cause of the slowness. In one office I worked we had a 7 day turn around time for one process. When a colleague and I looked into it there was no real reason for this delay, it was probably a legacy from a very old backlog. So the process looked like this;

Before ProcessLooking at it we realised that the actual process time was one day. All we had to do was clear the backlog and we could be turning around applications on the same day. Since the backlog is six days of work we asked our manager if we could both be put on working on the backlog full time for three days. It worked. We cleared the backlog, kept up with incoming applications and could move to same day service for all applications lodged before 3pm, and next morning collection for those lodged after 3pm.

This is a very simple example, but the steps are the same.

  1. Analyse the process, looking for the rate limiting step, this will usually be the step right after a build-up of product.
  2. look for the cause of the rate limiting step, this might require a deeper analysis in depending on the situation, the “five why’s” is one tool to help you get to the real right answer.
  3. Address that step, either by adding resources/equipment or by removing impediments or reducing the input.
  4. Check that the new process still runs smoothly, in the case above we had to get our manager and colleagues involved to make sure everyone stuck with the same day processing – bizarrely for some people it was difficult to understand that it was not more work.
  5. Go back to step 1 and look for the next rate-limiting step.

For more about how to think about rate-limiting steps I recommend the book “The Goal” by Dr Eliyahu M. Goldratt, it’s written in novel form and takes the reader through an analysis of a troubled manufacturing plant. Although it was first published in 1984 the principles still apply to any process.

And next time you’re out having a few drinks – pace yourself.

image; bottle necks / CC BY 2.0

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