The Challenger Disaster: Normalisation of Deviance

AKA: The Normalisation of Risk

In previous articles we’ve differentiated error into three types: slips and lapses, mistakes, and violations. This time, we’re exploring a certain type of violation called the “normalisation of deviance”, a term coined by Diane Vaughan. We often discuss this in our workshops when addressing failure patterns, particularly in safety critical organisations such as in healthcare, aviation, and heavy industry.

Diane Vaughan’s excellent book on the Challenger Space Shuttle disaster, “The Challenger Launch Decision,” explains the concept of the “normalisation of deviance” as: 

‘The gradual process through which unacceptable practice or standards become acceptable. As the deviant behaviour is repeated without catastrophic results, it becomes the social norm for the organisation.’

In other words, it’s the insidious process by which deviance from good practice, standards, policy or procedure becomes accepted as normal in an organisation. It’s not about breaking rules per se, though it may constitute that in practice; it’s the gradual and interpersonally “acceptable” process of a gap appearing from a condition to one where there is an increased level of risk. It is the social acceptance that what is happening now needn’t raise concern, because the increased level of risk has been normalised.

Neither does it mean any intention to cause harm, or recklessly risk harm (despite any potentially biased judgements after an event), because before an event occurs, we can’t see the gap occurring. This drift is normal, and occurs in nearly every organisation and context. And as such, it takes effort, focus, reflection, and psychological safety to detect and correct. Every time that we deviate from the “right” way or fail to follow protocol, it becomes easier to do it again next time – because it was fine last time. This is not just the cause of major incidents with long incubation periods – it’s also the reason most organisations function adequately day-to-day.

In the case of Challenger, it was that the rubber o-rings separating the sections of the Solid Rocket Boosters (SRBs) possessed a design flaw – under certain conditions, they would allow hot gas to escape, leading to potential disaster if this hot gas punctured the main fuel tank. However, because this flaw was known about, and because, over multiple launches, it had never so far actually resulted in disaster, it became “normalised”. A very strong cultural belief at NASA in redundancy (because there were two O-rings, one acting as a backup) led to a cultural mindset where even though the flaws were known, the resultant risk was tacitly considered acceptable.

Cultural Drift into Normalisation of Deviance

Normalisation of deviance occurs when people within an organisation become so desensitised to the deviant practice that it no longer feels wrong. This doesn’t happen overnight – it builds up over years and becomes part of the organisational culture, the substrate, usually in response to time or budget pressures, or simply a need to keep the boss happy. Vaughan describes the “long incubation period” prior to a disaster: every time that we deviate or fail to follow protocol, we skip a checklist or flick an alarm off, it becomes easier to do it again next time – because it was fine last time.

The O-ring issue at NASA began as a serious cause for concern, even a potential cause for halting a launch, but over time became more acceptable:

“A no-go recommendation below 53OF at the pad became “Lower temperatures are in the direction of badness for O-rings.””

Production Pressure

Vaughan described “production pressure” as a contributory factor to the Challenger disaster, which encouraged this normalisation of deviance, combined with scarcity (both of time and of money) and competition for funds as well as a degree of structural secrecy in the NASA organisation. This “production pressure”, or the desire to simply “get the job done” can overcome the desire to get it done safely or to a high quality, and this applies not just to Space Shuttle missions but to healthcare, technology, finance and many other domains too, as we’ll see later. 

In addition to production pressure, there are several reasons why deviance might become a norm:

1. Rules are seen as “stupid”, inefficient, or irrational. Of course, sometimes this is true.
2. Knowledge about the rules is not uniformly distributed. People might be unaware of a rule’s existence or might have been incorrectly taught the deviation from the rule as standard practice.
3. People intentionally break rules to achieve what they believe is a better outcome. In some cases, the rule might appear to hinder success, and again, sometimes this might actually be the case.
4. A lack of psychological safety means that people who observe or become aware of the violations don’t speak up or intervene. 

“Workarounds can occur when workers do not feel safe enough to speak up and make suggestions to improve the system.”

Amy Edmondson

Unfortunately, NASA did not adequately change its organisational culture following the Challenger disaster. This was demonstrated in 2003 when the space shuttle Columbia broke apart during re-entry, caused by a heat shield foam tile detaching from an external fuel tank during launch. Similar to the earlier O-ring problem, the issue with the heat shields was known but not treated with sufficient seriousness – over the preceding 22 years, this recurring issue had been normalised, leading to a complacency about the potential risk that it caused.

Since then, NASA have adopted and embraced the lessons learned from these two disasters, and describe in this piece how self-censorship (a lack of psychological safety) led in part to the disaster.

It’s been ok before, it will be again.

This phenomenon of cultural drift into risky practices demonstrated within Nasa is also found in other domains, including aviation, where we have the example of the 737 MAX disasters in 2018 and 2019. Evidence now shows that Boeing was aware of issues with the MCAS implementation since its first flight in 2016, but because nothing bad had so far happened (until the tragic crash of October 2018) there was no sense of urgency to correct the problem. It had become normalised.

Another example occurred in January 2012 with the Costa Concordia, a Carnival cruise ship, which capsized off the Italian coast, resulting in the loss of 32 lives. The captain deliberately strayed from the official route, a practice he and other captains had frequently engaged in to give people on the shore a show by passing close to an island, via an unapproved course. Investigative journalist Andrea Vogt noted that Carnival’s leadership ‘not only tolerated, but promoted and publicised the risky ship salutes off the island of Giglio and other tourist sites as a convenient, effective marketing tool.’ Thus, the deviance had become normalised: they believed it had always been ok in the past, therefore it would be in the future. 

Richard Feynman describes this belief in his assessment of the Challenger disaster in reference to the flaws in the O-ring design that had successfully made it through a number of launches: “Try playing Russian roulette that way: you pull the trigger and the gun doesn’t go off, so it must be safe to pull the trigger again.” And of course, in real life, it’s even more uncertain than that, because “we don’t even know how many bullets are in the gun.”

Psychological Safety

Vaughan describes how important psychological safety is in order to mitigate against the normalisation of deviance: 

[We must be] “clear about standards and rewarding whistleblowers. Also, create a culture that is team-based such that each person would feel like they were letting their colleagues down if they were to break the rules. Finally, the importance of a top-down approach to safety cannot be overstated. If the employees see executives breaking rules, they will feel it is normal in the company’s culture. Normalisation of deviance is easier to prevent than to correct.”

Related Articles:

Types of error

Normal Accidents

Chernobyl: Safety Cultures and Secrecy

Psychological Safety in Aviation

James Reason’s Swiss Cheese Model

Further resources on the normalisation of deviance:

Diane Vaughan’s “The Challenger Launch Decision”

Nasa: https://sma.nasa.gov/docs/default-source/safety-messages/safetymessage-normalizationofdeviance-2014-11-03b.pdf

In diving:  https://www.thehumandiver.com/blog/normalisation-of-deviance-not-about-rule-breaking

In the military: https://safety.army.mil/MEDIA/Risk-Management-Magazine/ArtMID/7428/ArticleID/7233/The-Normalization-of-Deviance

In healthcare: https://www.pslhub.org/learn/improving-patient-safety/human-factors-improving-human-performance-in-care-delivery/barriers/diane-vaughans-theory-of-the-normalisation-of-deviance-r1284/

In aviation: https://www.flightsafetyaustralia.com/2017/05/safety-in-mind-normalisation-of-deviance/

Human factors: https://humanfactors101.com/2016/08/09/normalisation-of-deviance/

“Bending The Rules: Managing Violation in the Workplace”: https://www.researchgate.net/publication/251529937_Bending_The_Rules_Managing_Violation_in_the_Workplace

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