Category Archives: warnings

HF/Usability Hodgepodge

Things too small for their own post but interesting nonetheless…it’s a hodgepodge, a mélange, a potpourri!

911: Trying to fight slips via warnings

I got a newsletter in the mail today from the City of Raleigh. Here are some excerpts centering on the problems with our area code:


What do a child playing with a telephone, an unprotected non flip cell phone and someone dialing a ten-digit phone number in the 919 area code have in common? They all can lead to inadvertent calls to 911.

As much as 10 percent of the calls to 911 are accidental calls. If you do accidentally dial 911, stay on the line and speak to someone to let them know there is no emergency. Otherwise 911 center staff will need to call back or send a police officer to investigate to determine if there is an emergency.

Ten-digit dialing coupled with living in the 919 area code means more people now dial numbers with the area code and ours is a prime candidate for a mis-dial and accidentally calling 911.

Ways to minimize the risk are to use caution when dialing numbers using the area code.

They provided good information, but I believe it’s likely that fighting the 919 area code is an un-winnable battle. So, when you accidentally dial it, don’t hang up!

If you need a moment of humor, watch this humorous video about changing the emergency number.

Electric Scooters and their Warnings: A Guest Post by Kim Wolfinbarger

Electric shopping carts are common in large grocery stores. Essential for users with mobility impairments, they are also helpful for pregnant women, elderly shoppers, and other who have trouble walking long distances.

A few months ago, my grandfather overturned such a cart in a parking lot and broke his hip. Interested in what might have caused the accident, I examined a similar cart at my local store.

in-storeWhile the cart appeared stable, red-and-white signs affixed to the inside and outside of the basket read, in large letters, “IN-STORE USE ONLY.” Two others warned, “INTENDED FOR USE INDOORS ON LEVEL SURFACES ONLY!” and “DO NOT TAKE THIS CART OUTSIDE THE STORE.” An instruction manual I found online had similar statements in several places.

instructionsHere is the problem: A customer who uses the cart while shopping will surely want to use it when taking groceries to the car. My grandfather lived independently and drove himself to the store, but rheumatoid arthritis made walking difficult. Using an electric cart made it possible for him to do his own shopping. While he most likely saw the warning, he may have dismissed it as a statement written to merely to discourage lawsuits. (This is speculation–he could not converse following the accident and died a few weeks later–but it is consistent with his personality.)

Clearly the manufacturer had anticipated that people would use the carts outside and thought this behavior might be hazardous.  But did the store share this concern? Since the cashier loaded the bags into his cart following the purchase, it appears that, despite the warning, the store expected him to drive the cart to the parking lot.


The signs and repeated warning statements in the manual suggest a mismatch between the design of the product and the expected behavior of users. So how should the problem be addressed?

  • If the carts are truly not stable outdoors, stores should not allow them to be driven into the parking lot. Instead, employees should carry out groceries for all customers who use a motorized cart.
  • Offering the service is not enough; some customers, not wanting to be a bother, will refuse assistance if asked. Instead, when the cashier begins checking out a customer with an electric cart, she should immediately summon a worker to load the groceries into a push cart and take the groceries to the customer’s vehicle.
  • Manufacturers should assume that customers will take electric carts outdoors and design them accordingly. Motorized scooters intended for outdoor use are widely available.
  • If they have not already done so, shopping cart manufacturers should implement similar stability features.  As human factors engineers have said for years, a warning is no substitute for good design.
  • Good warnings tend to have a “why” that informs the user about the hazard when that hazard is not immediately obvious. If you though the reason to keep the cart indoors was because you might be hit by a car, your decision to take the cart outdoors could be different than if you knew the cart were unstable.

Kim Wolfinbarger is the recruitment coordinator and an adjunct instructor for the School of Industrial Engineering, University of Oklahoma. Her research interests include usability, product design, industrial ergonomics and design for special populations.

1960′s Human Factors : The Titan II Missiles

I went on a trip to Tucson over the holidays and toured the last Titan II missile silo. A brief history: from 1963-1982 these missiles were part of the cold war “peace through deterrance” and “assured mutual destruction.” In essence, they provided one reason not to attack the US: even were we destroyed, these missiles would still launch to destroy the Soviet Union.

Politics aside, the control room and interfaces for these missiles were fascinating from a human factors perspective. Gauges, buttons, and rotary inputs reside where we now would expect screens and keyboards. I reflected on this while there: though you need a button for each function, at least the interface never changes.

I snapped the picture below as an example of users improving a system. It appears they are trying to reduce their memory demands by listing on labels the upper and lower boundaries of these controls. It reminded me of the draft beer handles added to the levers in a nuclear power plant (as discussed by Don Norman in “The Design of Everyday Things.“)

A little more history: The Titan sites do not have a perfect safety record. With 54 sites operating for almost 40 years, there were 4 recorded accidents, all where lives were lost and one early fire where 53 people died. Fortunately, none of these accidents resulted in a nuclear explosion, not even in one where the nuclear piece of the missile was blown out of the silo. This site provides a list and engineering analysis of the accidents, and I would be interested in a human factors analysis.

In the accident that ejected the nuclear warhead, the commonly reported story says the explosion occurred when the missile was being serviced and a repairman dropped a heavy tool on the fuel tank. This implies the explosion was instant, however it actually occurred over 8 hours later, as the fuel exited the breech. The best description I could find comes from a newspaper, the Arkansas Leader:

The missile was housed in a silo within a silo that consisted of eight levels. Maintenance crews were working on level two when the accident happened. Attached to the hydraulic standing platforms was a rubberized boot that flipped over between the missile and the platform to prevent anything from falling through if dropped.

The day missile 374-7 exploded, the boot didn’t keep the socket from falling. At 6:30 p.m., maintenance crews entered the silo to begin work after being delayed due to various unrelated equipment malfunctions. The eight- and three-quarter-pound socket fell, hit the standing platform and bounced toward the missile.

The boot had become too pliable through the years, and the socket fell 70 feet down the silo, hit the thrust mount and bounced into the side of the stage one fuel tank. The 100,000-gallon fuel tank emptied into the bottom of the silo. The fuels interacted and generated heat, which in turn increased the pressure on the tanks. At 8 p.m., the wing made the decision to evacuate the control center.

“When we did that, we had no readings and no way of telling what was going on out there,” Gray said. “We lost all readings,” Gray added.

Many attempts were made to get into the control center to see the readings, according to Gray. At 3 a.m., two people, Living-ston and Sgt. Jack Kennedy, made it into the complex. “When they made it in and had to back out because the fuel was so concentrated they couldn’t see, there was some controversy on who told them to turn on exhaust fan 105,” Gray said.

What that did, according to Gray, was pull the heavy concentration of fuel into the equipment area with all the electrical pumps.

“And automatically, boom!” Gray said. “The fire flashed back into the silo, which already had tremendous heat in there, and when the fire flashed back, the stage one oxidizer tank that was already very, very high in pressure, erupted.”

Within one hour of the accident, Gray found the nuclear warhead intact. “It was cracked, but it pegged out on the radio-activity scanner,” Gray said.

Lessons learned from this accident brought about security improvements near nuclear weapons. Security measures to prevent accidents include: all workers wearing a belt with lanyards to attach tools to, a cloth on the platform to reduce the chance of tools bouncing off the platform if they do fall and a renovation of the platforms.

One of our tour guides had actually been stationed at the silo. He was a great guide and a living piece of history. Consistent with what you might expect, he said the hardest times to keep the missile running and protected were the down times, hours of vigilance and inactivity.

Last, I also photographed some of the operation manuals at the museum. Apologies for the fuzziness of these pictures, and I’ll re-type the best bits:

7. Key Run Up procedure, if required. (figure 3-26C)….Performed

Reference SACR 100-24, Volume VI to determine if key run up is required.


Step 8 can only be performed when SYNC indicator is lighted in NORM modes or TRACK/TRSHD indicators are lighted in SPCL modes.


Observe printout on teleprinter. Printout is continuous series of characters RY’s or 64’s if transmitter site is transmitting idle message, or normal message traffic.

9. DEMODULATOR CONTROL PRINT MODE thumbwheel switch …Set as directed


*PVD must be continuously monitored visually or aurally.

*The PVD may be monitored by either a team in the silo or a crew member in the control center utilizing the wire type maintenance net.

For entry into launch duct level one, the PFC will be positioned outside of the opened level two launch duct access door, with sufficient probes to reach in the launch duct unless the PVD is required on level one of the launch duct for a sniff check.

Generally, I notice a large number of if/then/or/only types of commands.

I have only one last thing to say: the fact that Tucson, AZ, Damascus, AK and Wichita, KS are still around is a testament to the power of training and practice over our human frailties.

Terrifying Telephones

I purchased a new phone and wanted to understand how to do 3-way calling on it (you can’t). But that’s not the point of today’s post. This is the first page of the manual.

Probably only an HF professional interested in warnings would actually turn to page 38, and I went there straight away.

Click the image for the actual page, or continue reading just for the highlights.

1. Read and understand all instructions.

2. Unplug this product from the wall outlet and refer servicing to an authorized service facility under the following conditions:

D. If the product does not operate normally by following the operating instructions. Adjust only those controls that are covered by the operation instructions, as improper adjustment of other controls may result in damage and often requires extensive work by an authorized technician to restore the product to normal operation.

14. Avoid using a telephone(other than cordless) during an electrical storm. There is a remote risk of electric shock from lightning. (ed. this is a cordless phone)

16. Only put the handset of your telephone next to your ear when it is in normal talk mode.

(and then at the end:)

CAUTION: Use only the power adapter provided with this product. To purchase, visit our website at

Who Watches the Watchers?

Testing products can be a dangerous job, even when you are well aware of the potential hazards. Thanks to The Consumerist for pointing me to this blog entry at Consumer Reports.

Believe us when we say we are unapologetic sticklers for safety here at Consumers Union. We think about it and talk about it all the time, but that doesn’t mean that folks on our staff don’t make the occasional safety blunder….

…”I read with great envy our story on pressure washers a few years ago—this was before I even worked here—then ran out and bought one. The story explicitly said make sure you don’t point it at yourself. Our video even had a guy who had really hurt his foot that way, as I recall. “I’ll never do that,” I said confidently. And, sure enough, the first time I used the device I managed to just brush the edge of my wrist with the stream. No skin left. Scar—small one—still there today to remind me always to wear hand and eye protection and never point it at yourself!”

I just wish they wouldn’t keep saying “blunder”. However, in opposition to my usual diatribe about not blaming the user, I have to admit I laughed at this story:

“About 15 years ago I was finishing my basement. I put in the rough wiring for above-the-sink lighting, but didn’t tape off the end. A few nights later I was standing on a stool hammering close to the exposed wire. Make that too close. The metal cheek grazed the wire, tripped the circuit breaker and sent a numbing wave down my arm. I walked in the dark and reset the circuit breaker. Then, to distinguish myself from so many other do-it-yourself homeowners, proceeded to demonstrate to my wife exactly what happened. Exactly being the optimal word.”

Keep checking back at the Consumer Reports site, as they state this is only the first in the series.

Homeland security warnings

Found a link to this parody site of the homeland security symbols (via AskMetaFilter). This is my favorite symbol:

Michael Jackson is a smooth criminal

The images are real homeland security symbols.  In all seriousness, my friend Chris Mayhorn from North Carolina State University has researched these homeland security symbols and found that not everyone can interpret the real meaning of these warnings:

Mayhorn, C. B., Wogalter, M. S., & Bell, J. L. (2004).  Are we ready?  Misunderstanding homeland security safety symbols.  Ergonomics in Design, 12, 6-14.