How Poka Yoke Improves Safety

Thousands of workers die or get injured on the job in the US each year. Workplace injuries and fatalities are financially and socially  [PDF] costly. 

Safety features are at the forefront of most product design. No one wants to be the reason a customer was hurt or killed because of poor quality or a dangerous feature went unnoticed. Rigorous testing is required to ensure all the uses and possible lengths of product lifetimes are discovered before customers even get their hands on something. It is the unsung hero of industry – if the job is done correctly, you will never hear about it.

Problems arise, however, when things that are designed to be safety features have failures that cause injury or fatalities.

It will never be possible to predict every single use of a product but companies do employ certain methods of attempting to drastically reduce the possibility of failure. Six Sigma and Poke Yoke were two methods developed by industry leaders to reduce waste and defects.

Six Sigma was developed by Motorola and Allied Signal. It is a disciplined and data-driven approach and methodology for getting rid of defects in any process from the manufacturing process all the way to service. This was successfully implemented in 1995 by General Electric and they estimate cost savings of $10 billion in the first five years of implementation. 

The objective of Six Sigma is the implementation of a measurement strategy that focuses on process improvement and variation reduction through improvement projects. The DMAIC process (define, measure, analyze, improve, control) is for existing processes that fall below specification and businesses are looking for incremental improvement. The DMADV process (define, measure, analyze, design, verify) is used for new processes or products. Specialists who oversee these processes are called Six Sigma Green Belts and Six Sigma Black Belts and are overseen by Six Sigma Master Black Belts. Consultants have developed proprietary methods for implementing the Six Sigma quality and have saved approximately $230,000 per project, according to the Six Sigma Academy.

Poka Yoke is another method designed to draw attention to and prevent the occurrence of defects. Off-spec conditions are addressed early in the process so any costly defects in the final product are significantly reduced. Poka Yoke can also refer to features in final products that are meant to ensure safe and effective usage.

The term was first used by Toyota as they were developing fool-proofing methods in their production lines. When implemented properly, Poka Yoke improves quality and reduces costs related to poor quality by ensuring each stage in the development chain maintains the proper quality so defects never reach the customer, a very costly mistake. Repair, warranty claims, scrapping, customer dissatisfaction, obsolescence, labor, raw materials, and utilities are all related costs to defects that make it all the way to the end of the development and product chain.

The failure to identify threats is very real and can have incredible consequences, for your business and lives of your customers. There are four infamous examples below of products that suffered catastrophic product failures, some with fatalities.

Takata PSAN air bags – Even ten years after this recall began, there are still over 62,000 people driving with these air bags, most in older-model cars that have been bought and sold several times and owners either ignored the recall warnings or never received them, according to Honda, who is one auto manufacturer that uses them. The recall involves more than 37 million vehicles built by 19 automakers. Worldwide, at least 22 people have been killed and hundreds more severally injured when the airbags exploded and sprayed shrapnel. Driver-side air bags in Hondas have a 50% chance they will explode on impact.

The worst among the bad bags are known as Alphas, driver-side air bags installed in Hondas that have up to a 50% chance they will explode on impact. The US Department of Justice fined Takata $1 billion for not being forthcoming with information during the investigation.

Tylenol – In a still-unsolved crime in the fall of 1982 in Chicago, seven people died after taking Extra-Strength Tylenol that had been laced with potassium cyanide. It sparked panic for days, with police cruising the streets and blaring warnings to discard the product. Then the copycats came out. Over the next month, 270 different incidents of product-tampering were recorded, from pins in Halloween candy to Excedrin laced with mercuric chloride. Parent company Johnson & Johnson spent millions of dollars recalling Tylenol from all stores across the country. New tamper-proof seals were then mandated by the FDA for over-the-counter drugs after this.

Lithium-ion batteries – Ensuring that your whole product is sufficiently tested together is crucial, especially if you are using parts from other manufacturers. In 2006, Dell had to recall more than four million laptop computers because the Sony lithium-ion batteries posed a fire threat due to excessive overheating. It was predicted that the recall cost Dell and Sony a combined $400 million. The Federal Aviation Administration grounded U.S.-registered Boeing 787-8 airplanes due to a fire aboard caused by the lithium-ion batteries. It was not a traditional product recall but the loss of the aircraft in service to the airlines that used them had a major impact on Boeing and its customers. 

Firestone Ford Tires – Nearly 175 fatalities and over 700 injuries were attributed to Bridgestone/Firestone tires and sparked a recall of 6.5 million tires in 2000. The treads on some of the Firestone models would peel off and cause the tires to blow out, which would in turn cause certain cars and SUVs to roll over. Later that same year, Goodyear treads separated in some light trucks and were also linked to approximately 120 injuries and 15 fatalities.

Safety features are supposed to give consumers and product users a level of comfort that they can be secure while going about their day. Failure to follow manufacturing and design protocols can have ghastly results for life and your business. Employing techniques such as Six Sigma and Poka Yoke can certainly help avoid most mistakes but humans will never be infallible. Minimizing damage and injury gets more certain increased testing along the entire product lifecycle.