mistakeproofing, poka yoke: The practice of designing products and processes to eliminate (or at least to reduce)
the likelihood of occurrence of mistakes, and thereby avoid creating defects (or reduce their severity).
What is Mistakeproofing?
Shigeo Shingo (1986), a master mind of the Toyota Production System, introduced the concept of “poka yoke” (Japanese) or “mistake proofing” (English) in his book titled Zero Quality Control: Source Inspection and the Poka-yoke System. This concept goes hand-in-hand with the concept of “jidoka” (Japanese) or “autonomation” (English) as together they form a pillar of the Toyota Production System.
Autonomation refers to machines built to detect problems and stop by themselves, so as to “relieve the burden of constantly supervising a machine, and allow [people] to use their talents for more beneficial things (like adding value)” (Liker and Meier 2006 p. 177). “The purpose of autonomation is the rapid or immediate address, identification and correction of mistakes that occur in a process… Once the line is stopped, a supervisor or person designated to help correct problems give immediate attention to the problem the worker or machine has discovered. To complete jidoka, not only is the defect corrected in the product where discovered, but the process is evaluated and changed to remove the possibility of making the same mistake again. This ‘mistakeproofing’ of the production line is called poka yoke.” (Superfactory 2008).
Shingo’s premise of “zero quality control” is to “do it right the first time,” but Shingo also states (p. 82): “I claim that it is impossible to eliminate all errors from any task performed by humans. Indeed, inadvertent errors are both possible and inevitable. Yet errors will not turn into defects if feedback and action take place at the error stage. Zero defects can be achieved because errors do not turn into defects (op. cit. p. 84) thanks to the use of a combination of source inspections and self-check systems.
Bodek stressed in his preface to Shingo’s book (1986 p. vii) that we should “drop the idea that defects are a normal part of manufacturing.” In the AEC industry, the notion that zero QC is contrary to the reliance of practitioners on inspection and punch lists as means to work towards an acceptable end product, hopefully one that is satisfactory and of quality!
To eliminate the need for quality control, the practice of mistake proofing sets out to prevent errors or defects from occurring in the first place.
Mistake proofing is particularly well suited for the AEC industry with its low-volume and mixed production systems where statistical quality control methods cannot be implemented due to lack of data and un-timeliness of findings that result from after-the-fact data processing. Mistake proofing requires a different way of thinking about production processes and its constituent operations, but once practitioners have learned to recognize mistake proofing devices, their new mind-set will enable them to spot numerous opportunities available to mistake proof their workplace. They will find that many mistake proofing practices can be implemented at a minimal cost, though some do require investment in new product development.
Examples of Mistakeproofing Practices
|Color coding of design drawing shows different wall types for drywall cost estimate (Source: DPR, Inc., Camino Medical Project)|
|Color coding shows locations for sheet metal straps and pipe hangers on metal decking
(Source: John Mack, Southland Industries, Inc., presentation at 2007 LCI Annual Conference, San Francisco, CA)
|The heads of these pneumatic nails have different colors to correspond to different lengths and diameters. This makes it easy to verify whether or not nails were installed according to a nailing schedule. Source: Hawks, J. “Tool Review: Color-Coded Pneumatic Nails.” Fine Homebuilding Magazine reprinted on http://www.taunton.com/finehomebuilding/pages/h00090.asp visited 5/23/06.|
Adaptability and Matching
|Flexible water hose
(Source: Picture by Iris D. Tommelein, Boston, MA, 2007)
|Connect plug and wiring of light fixtures (Source: Finelite product literature)|
|Sealant and return leg to guarantee roof performance (Source: Butler manufacturing product literature; http://www.butlermfg.com/images/level3_pages/returnleglink-large.jpg visited 5/23/06).|
Mistakeproofing: A Mindset and Practice to Improve Construction Occupational Safety and Health
We completed a research project on “Mistakeproofing the Design of Construction Processes Using Inventive Problem Solving” (Tommelein and Demirkesen 2018) with funding from the CPWR. An overview and findings of the research are presented next. A summary is posted at https://www.cpwr.com/sites/default/files/publications/KF2018-mistakeproofing-OSH.pdf and the report itself may be downloaded from http://bit.ly/2HcDgv1 .
For more information contact Iris D. Tommelein at email@example.com
“Mistakeproofing” is the use of any device or method that either makes it impossible for an error to occur or makes the error immediately obvious once it has occurred. The objective of mistakeproofing is to reduce or eliminate the occurrence of errors, as they cause resource waste and defects. Mistakeproofing includes both labor and management: everyone can help identify opportunities to reduce or eliminate errors by applying mistakeproofing tools and practices through creative problem-solving. The authors explore how mistakeproofing applies in construction to reduce incidents and worker injuries, which are substantial sources of waste in the industry as they interrupt production, cost lost workdays, or result in other harm.
- The principles of mistakeproofing offer practical and useful application in the construction industry. Their systematic pursuit is bound to help improve quality performance, including safety and health performance.
- Quite a few applications of mistakeproofing already exist in the construction industry. Documentation of existing practices will inspire greater adoption of mistakeproofing.
- Developing a mistakeproofing mindset starts by raising awareness and empowering people to experiment with devices or methods in pursuit of continuous improvement. Training will be needed to foster a mistakeproofing mindset.
- The generation of new ideas on how to mistakeproof certain product or process designs can be supported by drawing on the principles of TRIZ (Theory of Inventive Problem Solving).
- The six principles of mistakeproofing align to some degree with the five levels in OSHA’s Hierarchy of Controls, in that both prioritize elimination and substitution of practices subject to human error.
Bodek, N. (1986). Page vii of Publisher’s Preface to Shingo (1986).
dos Santos, A. and Powell, J. (1999). “Potential of poka-yoke devices to reduce variability in construction.” Proc. 7th Ann. Conf. Int’l. Group for Lean Constr., Berkeley, CA, pp. 51-62.
dos Santos, A., Powell, J., and Formoso, C.T. (1999). “Evaluation of Current Use of Production Management Principles in Construction Practice.” Proc. 7th Ann. Conf. Int’l. Group Lean Constr., Berkeley, CA, pp. 73-84.
dos Santos, A., Powell, J., Sharp, J., and Formoso, C.T. (1998). “Principle of transparency applied in construction.” Proc. 6th Ann. Conf. Int’l. Group for Lean Construction, Guaruja, Brazil.
Finelite (2001). The Affordable Alternative – Contractor Guide. Finelite Inc., Union City, CA, http://www.finelite.com/, 20 pp.
Finelite (2008). Estimator and Contractor Guide. Available online at http://www.finelite.com/contractor/ContractorGd_m.pdf visited 22 April.
Grout, J. (2007). Mistake Proofing the Design of Health Care Processes. AHRQ, available online at http://www.ahrq.gov/qual/mistakeproof/mistakeproofing.pdf
Liker, J.K. and Meier, D. (2006). The Toyota Way Fieldbook. McGraw-Hill, 475 pp.
Shingo, S. (1986). Zero Quality Control: Source Inspection and the Poka-yoke System. Productivity Press, Cambridge, Mass.
Superfactory (2008). Website http://www.superfactory.com/topics/jidoka.htm visited on May 5th.
Tommelein, I.D. (2008). “‘Poka Yoke or Quality by Mistake Proofing Design and Construction Systems” In Tzortzopoulos, P. and Kagioglou, M. (Eds.). Proceedings of the 16th Annual Conference of the International Group for Lean Construction (IGLC 16), 16-18 July, Manchester, UK.
Tommelein, I.D. and Demirkesen, S. (2018). “Mistakeproofing the Design of Construction Processes Using Inventive Problem Solving.” CPWR Report, February, http://bit.ly/2HcDgv1