Category Archives: safety

Tylenol: A narrow margin of safety

I’m always surprised at how many people don’t know how dangerous Tylenol (or anything with acetaminophen/paracetamol) is. I can’t remember where I initally learned that just a few pills could cause liver failure, but it was at least 10 years ago. Of course, more than 10 years ago, I remember that Tylenol was the only painkiller allowed to be given out in my high school because it was so “safe.”

Anyway, it’s certainly been in the news lately and I have collected some interesting sources. First off, This American Life devoted an hour to investigating the problem, its history, and ongoing conflict. Absolutely worth a listen. Here is a teaser bit of the transcript:

Will Lee is one of the liver specialists and researchers who’s been calling attention to the dangers of acetaminophen. He is at the University of Texas Southwestern Medical Center and talked to reporter Sean Cole.

Will Lee: In one of the articles, we actually printed up the little coupon that I got with my Zocor prescription that says, $2 off on your next acetaminophen bottle. And one of the things on the coupon, it says safest. Not safer, or not safe, but safest. Well, this is the number-one drug killing Americans every year.

Sean Cole: Over-the-counter drug killing Americans.

Will Lee: Over-the-counter drug.

Sean Cole: Not the safest.

Will Lee: Not the safest, for sure. So I guess that’s– if you think I have a bee in my bonnet, that’s probably where it came from.

There are two human factors issues related to this “narrow margin of safety” that I’d like to highlight:

1. Warning design
2. Counter-intuitive doses for children


If you’d like a good overview of warning design, see Wogalter, Conzola, & Smith-Jackson, 2002.

The warnings are printed in red on the lid of the container and say “Contain acetaminophen – Always read the label.”
I know it took a long time to even have this, but I’d like to point out that this does not follow the best practices for warning design because it does not include the consequences or focus on the “hidden hazard.” Hidden hazards are really the reason warnings are important. Here are some examples:
  1. Does a knife need a warning that it is sharp? No, that’s not a hidden hazard. Now, if the knife is SO sharp it’s unexpectedly dangerous, then it needs a warning that conveys that information. I had a friend in high school who had a habit of testing knives with his fingertip. This never cuts you, just gives a feel for sharpness. Well, one time he had someone sharpen a swiss army knife for him – and what usually would have “felt sharp” went instantly through the skin down to the bone. That’s a hidden hazard.
  2. Does coffee need a warning that it’s hot? No, not if it’s just drink-ably hot. But yes if it is purposefully super-heated enough to cause 3rd degree burns. Watch this video to get new insight on the McDonald’s coffee story.

It is the narrow margin of safety that is the hidden hazard of acetaminophen. Nothing else available over the counter can kill you with such a small increase in dose. You can take 20x the recommended dose of Advil before it becomes threatening. I ignored the dosing for Advil once and took 6 in 3 hours rather than 2 – it made me sick and I regretted it, but would I deserve to die for that mistake? I could have died if it had been Tylenol instead of Advil. This hidden hazard is the most critical part of the warning – even if it’s on the label, I think it should be highlighted on the lid.

Which brings me to… the hidden hidden hazard that was created by the Tylenol company.

Counter-intuitive doses for children
In brief, for over a decade Tylenol provided medication labeled for infants and medication labeled for children (and of course, medication for adults). 99/100 people on the street would assume that these were in order of strength – least for the infants, more for the kids, and most for the adults. That assumption was correct for the kids and the adults. The counter-intuitive dose was for the infants: instead of being weaker because they were smaller, it was much higher. Their reasoning was that it is hard to get medication into an infant, so if it’s stronger you can get an effect with less. An article from Pro-Publica gives a more detailed summary.
An excerpt from Pro-Publica:

The two types of pediatric Tylenol had a counterintuitive difference. Drop for drop, the strength of Infants’ Tylenol far exceeded that of Children’s Tylenol.

In addition, the active ingredient in Tylenol, acetaminophen, has what the FDA deems a narrow margin of safety. The drug is generally safe at recommended doses, but the difference between the dose that helps and the dose that can cause serious harm is one of the smallest for any over-the-counter drug.

By confusing the pediatric products and administering too much of the infants’ version, parents could inadvertently overdose their children. Other manufacturers also made two children’s products with different concentrations of acetaminophen.

Between 2000 and 2009, the FDA received reports of 20 children dying from acetaminophen toxicity – a figure the agency said likely “significantly underestimates” the problem. Three deaths were tied directly to mix-ups involving the two pediatric medicines. Such errors may have caused some of the other deaths, but the agency has acknowledged that its data lacks sufficient detail to determine the precise cause.

This American Life included a heartbreaking case where parents were instructed to give their infant doses measured in terms of the children’s Tylenol (their doctor just said “Tylenol”), but since they had an infant they did what anyone would and used the Tylenol for infants, resulting in the death of their baby.

The big push seems to be for better warnings (with the example in the picture as “better.”) Indeed, this can have an impact – for example, as reported in the NY Times, removing infant versions of medication and saying a drug is “not for children under 2” reduced drug-related emergency room visits for that age range by half.

Excerpt from the NY Times article:

In 2007, amid mounting concern that infant cough and cold medicines were unsafe and misused, manufacturers voluntarily withdrew products intended for children younger than 2. The makers revised the labels on the rest of the medicines, which now warn parents that they should not be given to children younger than 4.

Government researchers said on Monday that those moves have had a remarkable effect: a significant decrease in emergency hospital visits by toddlers and infants with suspected medical problems after using these medicines.

Dr. Daniel Frattarelli, a former chairman of the committee on drugs at the American Academy of Pediatrics, praised the study, saying it showed that “the label is a very powerful tool for changing parent behavior.”

In the new study, published in the journal Pediatrics, researchers at the Centers for Disease Control and Prevention reviewed data from 63 hospitals to estimate the number of emergency visits from 2004 to 2011 by young children who had taken cough and cold medicines.

Children under 2 accounted for 4.1 percent of all emergency visits for suspected drug-related effects before the 2007 withdrawal, the researchers found, and accounted for 2.4 percent afterward.

However, even casual readers of the blog have probably noted how often I mention the Hierarchy of Safety: first try to design out the hazard, guard against the hazard, and warn. I’m not saying warnings aren’t important, but if we want to have the biggest impact we should be working on designing out or guarding against the hazard. Some ideas in that realm include bottle design that restricts the flow of liquid (this could prevent a child from dosing him or herself, but not parents from giving the wrong dose), and packaging “single servings” of medication, so that its obvious how much to give at one time. Although the treehugger in me isn’t a fan of more packaging, this also could provide more space for good warnings AND have those warnings in extremely close spatial and temporal proximity to use of the product.


Brilliant guard against accidents in indoor rock climbing

For those who don’t follow news of climbing accidents as closely as I do, there has been a spate of accidents associated with the automatic belay devices (autobelays) installed at climbing gyms.

These devices are handy to have around as they negate the need for a climbing partner, allowing one to exercise and train alone. The climber clips his or her harness into the device at the bottom of the wall, and it automatically retracts (like a seat belt) when you climb upward. At the top, you let go of the wall and the device lowers you slowly back to the ground. You are probably imagining that the accidents had to do with failures of the equipment – while that is not unheard of, the most recent issues have all been with climbers forgetting to clip into the system at all.

The most recent tragedy occurred this past September, where an experienced climber died after a fall in a Texas gym, and it’s been listed as so common it happens at “every gym,” though not always resulting in a fall. Here is the facebook page with members of another gym discussing a similar accident.


If you talk with climbers or read accident forums you will invariably be faced with a large contingent bent on blaming the victim. I’ll grant that it is hard to imagine forgetting to clip into a safety device and climb 30 feet up a wall, but that’s because I hardly ever do it. One characteristics these accidents share is that the victims were experienced and used the auto-belays frequently.

When a procedure becomes automatic, it becomes more accurate and less effortful, but it also becomes less accessible to the conscious mind. When a step is skipped, but all other steps are unaffected, it’s especially hard to notice the skipped step in an automatic process. If caring more or working harder or “being more careful” could actually prevent this type of problem, we wouldn’t have any toddlers left in hot cars, perfectly good airplanes flown into the ground, or climbers falling because they didn’t clip into the autobelay.

That brings me to the device I saw installed at a climbing gym last night.

guardAbove: The guard in place, clipped to the wall and ready to go. Notice how it blocks the footholds of the climbs.

photo 2Above: Nikki shows how to unclip the guard before attaching to her harness.


photo 4Above: Clipped in and safely ready to go. Guard is on the ground and out of the way (it is ok to step on it!)

Let me tell you why I think this is brilliant.

  • It’s highly visible.
  • It functions as a guard. This adheres to the hierarchy of safety: First, try to design out the hazard. Second, guard against the hazard. Last, warn. These are in order of effectiveness. Prior to this device, I had only seen signs on the wall saying “Clip in!” (And a year ago, even those didn’t exist.) This device physically blocks the start of the climbing routes, demanding interaction before one starts climbing.
  • Using it properly does not add any additional time or mess to climbing a route. If it weren’t there, the climber would still have to unclip the autobelay from an anchor close to the ground, etc. With it there, the climber does the same thing and once done, the guard becomes a flat mat that doesn’t get in anyone’s way.

Is it perfect? No. You can also climb with a belayer on the same or nearby routes, and then it’s also blocking your way at the start of the climb. Some adaptation should be made by the route-setters at the gyms to minimize this. But overall, what a great and simple solution.


Potpourri–Lazy Summer Edition

It’s summer and we (along with some of you) are taking a break.  But here’s a list of interesting usability/HF-related things that have crossed my path:

  • After much complaining, Ford is bringing back physical knobs in their MyTouch in-car controls.  Anne and I worked on some research (PDF) in our past lives as graduate students that directly compared touch-only interfaces to knob-based interfaces so it’s nice to see it is still a major issue; if only Ford read our 9 year old paper 🙂
  • Trucks driving under very low bridges is such a large problem in Australia that they are deploying a really novel and clever warning system.  A waterfall that projects a sign that’s hard to miss!
  • tags_finderApple will introduce their next version of OSX in the fall. One of the features i’m most excited about is system-level tag support.  Tags allow users to organize their files regardless of location or type.  I’m particularly interested in personal, single-user-generated tagging (compared to collaborative tagging like that used in flickr) as it appears to benefit older adults information organization and retrieval (PDF).  This pleases me.

Recent developments in in-vehicle distractions: Voice input no better than manual input

A man uses a cell phone while driving in Burbank, California June 25, 2008. Credit: Reuters/Fred Prouser
Earlier this week the United States Department of Transportation released  guidelines for automakers designed to reduce the distractibility of in-vehicle technologies (e.g., navigation systems). :

The guidelines include recommendations to limit the time a driver must take his eyes off the road to perform any task to two seconds at a time and twelve seconds total.

The recommendations outlined in the guidelines are consistent with the findings of a new NHTSA naturalistic driving study, The Impact of Hand-Held and Hands-Free Cell Phone Use on Driving Performance and Safety Critical Event Risk. The study showed that visual-manual tasks associated with hand-held phones and other portable devices increased the risk of getting into a crash by three times. [emphasis added]

But a new study (I have not read the paper yet) seems to show that even when you take away the “manual” aspect through voice input, the danger is not mitigated:

The study by the Texas Transportation Institute at Texas A&M University was the first to compare voice-to-text and traditional texting on a handheld device in an actual driving environment.

“In each case, drivers took about twice as long to react as they did when they weren’t texting,” Christine Yager, who headed the study, told Reuters. “Eye contact to the roadway also decreased, no matter which texting method was used.”

Begging robots, overly familiar websites, and the power of the unconscious?

Hello readers, and sorry for the unintentional hiatus on the blog. Anne and I have been recovering from the just-completed semester only to be thrown back into another busy semester.  As we adjust, feast on this potpourri post of interesting HF-related items from the past week.

In todays HF potpourri we have three very interesting and loosely related stories:

  • There seems to be a bit of a resurgence in the study of anthropomorphism in HF/computer science primarily because…ROBOTS.  It’s a topic I’ve written about [PDF] in the context of human-automation interaction.  The topic has reached mainstream awareness because NPR just released a story on the topic
  • The BBC looks at the rise of websites that seem to talk to us in a very informal, casual way.  Clearly, the effect on the user is not what was intended:

The difference is the use of my name. I also have a problem with people excessively using my name. I feel it gives them some power over me and overuse implies disingenuousness. Like when you ring a call centre where they seem obsessed with saying your name.

Product Confusability: Tide Pods

Kim Wolfinbarger sends along a new case of dangerous things being confused for food (the story is the same but the actors different, see previous examples).  Before you reflexively say, “only an idiot would confuse the two,” remember that 5-year olds don’t know the difference.  First rule of HF-club: you are not the user (or victim):

In California alone, 307 cases of accidentally ingestion of laundry packs by young children have been reported this year. And the cases in California, and nationwide, aren’t just limited to toddlers snarfing Tide Pods. When the product was released, Tide rivals such as All and Purex launched their own single-dose detergent capsules as well. Earlier this summer, Tide reconfigured the packaging of the product, adding a double-latched lid to the plastic tubs containing the Pods to make it more difficult for children to tamper with. Still, the number of reported incidents continues to climb along with news stories warning parents to take caution.

Just yesterday, Consumer Reports reported on a wave of Tide Pod-related poisonings in Glasgow, Scotland while the New York Daily News published a quick article stating that in New York City alone, 40 children have been hospitalized after eating the packs since April. TODAY also just published a piece on the alarming trend in which Ken Wahl, medical director for the Illinois Poison Center states: “I’ve never seen a consumer product that had that degree of injury in a child.”
Dishwashing detergent also comes in pod-like single serving doses but I am not aware of similar cases of ingestion.  Maybe it’s the coloring (they tend to be blue/green) or size (they are a bit larger I think)?

Collection of Aviation Safety Articles & Student Activity Ideas

I recently came across an impressive collection of Human Factors related safety stories, mostly concerning aviation, from a the System Safety Services group in Canada. The summaries are written in an accessible way, so I recommend this site for good classroom examples. I was already thinking of a classroom activity, perhaps for an undergraduate course:

In class:
Please read the following excerpt (abridged) from Aviation Human Factors Industry News Volume VII. Issue 17. Provide a list of the pros and cons of allowing ATCs to take scheduled naps during their shifts. Put an * by each pro or con that is safety related. The full article is available via the link above.

…the FAA and the controllers union — with assistance from NASA and the Mitre Corp., among others — has come up with 12 recommendations for tackling sleep-inducing fatigue among controllers. Among those recommendations is that the FAA change its policies to give controllers on midnight shifts as much as two hours to sleep plus a half-hour to wake up. That would mark a profound change from current regulations that can make sleeping controllers subject to suspension or dismissal. Yet, at most air traffic facilities, it’s common for two controllers working together at night to engage in unsanctioned sleeping swaps whereby one controller works two jobs while the other controller naps and then they switch off…

More than two decades ago, NASA scientists concluded that airline pilots were more alert and performed better during landings when they were allowed to take turns napping during the cruise phase of flights. The FAA chose to ignore recommendations that U.S. pilots be allowed “controlled napping.” But other countries, using NASA’s research, have adopted such policies for their pilots. Several countries — including France, Germany, Canada and Australia — also permit napping by controllers during breaks in their work shifts, said Peter Gimbrere, who heads the controllers association’s fatigue mitigation effort. Germany even provides controllers sleep rooms with cots, he said. …fatigue affects human behavior much like alcohol, slowing reaction times and eroding judgment. People suffering from fatigue sometimes focus on a single task while ignoring other, more urgent needs.

One of the working group’s findings was that the level of fatigue created by several of the shift schedules worked by 70 percent of the FAA’s 15,700 controllers can have an impact on behavior equivalent to a blood-alcohol level of .04, Gimbrere said. That’s half the legal driving limit of .08. “There is a lot of acute fatigue in the controller work force,” he said. Controllers are often scheduled for a week of midnight shifts followed by a week of morning shifts and then a week swing shifts, a pattern that sleep scientists say interrupts the body’s natural sleep cycles.

At home:
Your homework assignment is to identify another work domain with similar characteristics where you believe fatigue is a safety concern. Write an argument for requiring rest during work hours or other solutions for fatigue. Again, specifically call out the pros and cons of your solution.

A list of all articles, in newsletter form, can be found here.

Photo credit mrmuskrat @ Flickr

Bad Usability Causes Cranky Babies

I peripherally heard about another Tylenol recall and assumed the recall was prompted by tainted medicine or something.  Anne just sent me a link to the story and it is apparently usability related.  The syringe-based dosing system, called SimpleMeasure, seems to be difficult to use.  Here is what NPR says:

the “SimpleMeasure” dosing system that’s supposed to make it easier to fill a syringe with the right amount of the grapey painkiller and fever-reducer is too complicated for some parents.

Looking down the barrel of a gun

Here is a design that requires disobedience of the fundamental rule in a sport: don’t point your gun at someone you don’t plan to shoot. Blogger Mark Shead posits it might be due to a lack of domain knowlege by the designer and extends the analogy to software design.

Mistakes in software design aren’t always as easy to spot, but often it comes down to the same thing. To design something you must have at least a basic level of domain knowledge.  That doesn’t means you have to be a world famous chef in order to write a recipe webapp, but you need to make sure you at least know the basics.

Read the full post discussing this design.