# Geeks On Ice [Update]

Slashdot brings us a story about An Algorithm To End The Lines For Ice At Burning Man:

Any gathering of 65,000 people in the desert is going to require some major infrastructure to maintain health and sanity. At Burning Man, some of that infrastructure is devoted to a supply chain for ice. Writes Bennett Haselton,
The lines for ice bags at Burning Man could be cut from an hour long at peak times, to about five minutes, by making one small… Well, read the description below of how they do things now, and see if the same suggested change occurs to you. I’m curious whether it’s the kind of idea that is more obvious to students of computer science who think algorithmically, or if it’s something that could occur to anyone. Read on for the rest; Bennett’s idea for better triage may bring to mind a lot of other queuing situations and ways that time spent waiting in line could be more efficiently employed.

I skipped burning man this year but went for the first time in 2013. One of the only goods for sale at Burning Man is bags of ice — to keep your own food cool, or simply to refresh yourself, you can line up to buy bags of ice that are sold by Arctica camp out of the back of a refrigerated truck under a tent. Bags cost \$3 apiece.

photo: Nellie Bowles

During peak times last year, the lines were up to an hour long. This year, so I heard, the lines on the first day were even worse, because two of the three distribution points were unable to open due to closed roads, so everybody lined up at the only sales tent that was operating.

Regardless of the conditions, the procedure when you get to the front of the line is the same. You specify how many bags of ice you want, and deposit cash in a container on the counter. Then a volunteer walks back to the ice truck to fetch one or more bags from the truck and brings them back to the counter. You collect your bags and continue on your way.

OK, before reading any further — based on what I just wrote, can you think of a way to speed up the line? No cheating — read the preceding paragraph and think of what you might do differently. Spoilers follow!

The thought that occurred to me almost immediately after I got my bag of ice, was: Why not just have the volunteers carry the bags of ice from the truck to the counter, before people place their order? As long as the line is moving, no bag of ice would sit on the counter long enough to melt. And then each transaction at the front of the line would be reduced to: Customer pays for bag(s), customer picks up bag(s) and leaves. By eliminating the time to walk back to the truck and fetch the bag(s), the system would significantly reduce the per-customer transaction time.

I’d asked a handful of Burning Man veterans about this, and they said that Arctica had tried this at one point, but was required to stop by Nevada health code regulations, which treated ice as a “food product” and therefore said that it could not be moved out onto the counter until an order has been placed. This sounded puzzling to me — don’t cafés place other “food products” out on a counter all the time, where they can be bought and picked up by customers? And for the ice bags, why would it matter in practice anyway — even if the state of Nevada is worried about germs starting to multiply as soon as the bag is removed from the refrigerated truck, the time the bag spends sitting on the counter is still negligible compared to the time the customer spends transporting it back to their own camp.

So I emailed the Nevada State Health Division to ask them what the regulations actually said, and if they would allow the ice vendors to load bags of ice onto their sales counter before they had been paid for by a customer. One of their Public Health Engineers replied and said, “I can assure you that we do not require the ice to remain in the truck until it is ordered” (and dryly added, “It is common for vendors to blame the health authority for imagined regulations”). Regarding the resulting long lines, he also advised me, in the spirit of Burning Man radical self-reliance (if not practicality), “You may consider bringing your own ice to the Playa rather than purchasing it from them.”

So that’s it. There’s no regulatory reason why the ice can’t be brought to the sales counter before it’s paid for — where it wouldn’t even have time to start melting, if there are customers eagerly waiting to carry it away — and no reason why the line couldn’t probably move 5 to 10 times faster as a result. (I emailed Arctica to ask if they would start having volunteers bring ice bags up to the counter before customers place their orders, and showed them the email from the Nevada Health Division saying it would be legal. I received a very friendly reply, mostly asking me who I was and why I was concerned about the issue; I said I had no stake in the matter except hoping to reduce the wait times and hence the aggravation and health risks for people waiting in line in the sun. I have not received a reply to any subsequent inquiries after that.)

In a previous article I’d theorized about an algorithm for speeding up the vehicle exodus at Burning Man. (Basically, have a “priority lane” where cars can exit at different times of day, depending on the last character on their license plate. So one hour where the priority lane is set aside for cars whose license plates end in “A”, another hour where the lane is used by cars with plates ending in “B”, and so on. This means that drivers who want to use the priority lane, can just wait for the designated hour, instead of spending five hours queueing up to leave.) That was intended more of an intellectual exercise, as a jumping-off point for a discussion about which algorithms would work best under different theoretical assumptions, and with only the small possibility that it might ever actually be implemented at the real event.

The call to speed up the ice lines is not an intellectual exercise. Unless there’s a non-obvious major problem with making this change, this is something that could be done the very next year, and would save people thousands of person-hours waiting in line in the sun.

My other suggestion would be to have a “turbo” line even faster than the main one, designed for people to complete each sales transaction in seconds. Every customer in the “turbo” line would be required to have exact change (or be willing to overpay and let the vendor keep the change), and every customer would be required to have their cash fanned out in their hand like playing cards when they got to the front of the line. (A volunteer could walk up and down near the front of the line to verify that people already had their cash displayed properly.) A transaction at the front of the line would simply consist of, “Three dollars — bag”, or, “Six dollars — two bags”, where the customer shows their fanned-out money, dumps it into the cash receptacle, and picks up one or more bags from the counter.

With or without the “turbo” line, at first it might seem like it would take extra labor to keep a supply of ice bags moving constantly from the truck to the counter, but that’s not the case. For a given number of bags to be sold, every bag has to be moved from the truck, to the counter, exactly one time. So the total amount of labor is always going to be the same, for a fixed number of ice bags. To have a steady supply of ice moving quickly from the truck to the counter, you might need to have more volunteers working at the same time, but that just means that rather than having 5 volunteers with one-hour shifts spaced throughout the day, you’d have those same volunteers working simultaneously to keep the bags moving.

With the lines moving that much more quickly, what if the ice bags run out halfway through the day? Hopefully the vendor can just send the trucks back out to fetch more bags of ice to be brought back in and sold in the afternoon. But even if they can’t — even if, for some reason, the number of ice bags sold per day has to be fixed at X — you’ve still done an enormous amount of good by reducing the wait time from 30-45 minutes to 5 minutes. Because you still sell the same number of ice bags, but you’ve eliminated the pointless deadweight loss of all the time the customers were previously wasting in line.

And if the vendors can bring in more ice whenever their existing stock sells out much faster, that’s a win too — regardless of whether they’re selling the ice for profit or just for altruistic motives. If they’re selling ice to help people, then selling more ice is better. If they’re selling ice for profit, then selling more ice is better, too.

I’m being fairly pedantic here because I want to make it clear that I think that I think there’s no counterargument to be made to this, under any combination of reasonable assumptions — whether the vendors can bring in more ice or whether they’re stuck selling a fixed number of bags per day; whether the goal of selling the ice is for altruism or to make a profit. Bring the ice out before it’s paid for, shave the transaction time down to the bare minimum of the customer paying money and then grabbing their ice bags, and everyone will be grateful they don’t have to wait an hour in the sun.

And if you’re an adventurer thinking about going to Burning Man, my tips for making it (slightly) easier include bringing your own cooler (separate from any food storage cooler) so that you can buy a bag of ice each day, dump it in the cooler, and have your own supply of ice water. That’s well worth it, whether the wait time in the ice line is five minutes or an hour.

Makes perfect sense to me. So, will it happen?

Like many suggestions for improvements to Burning Man, the first response is “NO”. We’re told “we tried that and it didn’t work” and “the authorities won’t let us do it”. Kudos to Bennett for doing the work to fact check these statements: sure enough, they’re false. There is no regulatory reason for making Burners suffer in queues in the desert.

Having applied his brainpower to the Exodus and Arctica lines, perhaps Bennett can now turn his grey matter to the Will Crawl problems. Hint: mailing tickets to the 20% of Burners coming from outside the US will halve the number of people who have to go to Will Call. Fewer people should mean shorter lines.

Will BMOrg listen to the Burner community, and try something new to make things better for their customers?

[Update 10/21/14 2:53pm] I posted a link to this story at Arctica’s Facebook group and got an official response. Perhaps unsurprisingly, the answer was “NO” and “it’s been tried before”.

Not a new idea. It’s what we used to do. Surprise, ice melts quickly in the desert. Even sitting in the truck with the freezer unit pumping out 20 degrees, ice melts with the doors open. Not as bad as sitting on a hot metal table though. *That* is why it stays in the truck until it is sold. How melted do you like your ice? Would you rather wait a few minutes longer to get what you paid for or get a half-melted bag now? Our volunteers put a lot of effort into providing you the best product, in the most timely manner. If people come at peak times (opening & lunch), we’ll be busy. If they come at other times, there’s hardly a wait.

We also got “you can’t do it because of health regulations” as a comment on our Facebook page. Katie sayeth:

The line is caused by high and indecisive burners. So sayeth a line wrangler & slinger!

Video

# Ice To A/C: Solar Power Air Conditioner

Homemade AC Air Cooling unit produces very cold air. 42F air (in an 80F room). items needed: ice chest (hard-sided or styrofoam), pvc pipe, small fan and ice. (small solar panel is optional). great for space cooling. 3 ways to power it: a solar panel, a battery or an automobile (using 12v socket “cig. plug”). According to a top-rated AC company, this air cooler combines the durability of the “5 Gallon bucket air cooler” with the extra cooling power of the “styrofoam ice chest air cooler”. specs: fan: 12VDC 10w 0.8A. solar panel: 15 watt (1 amp). works best in semi-dry or dry climates. (drier air cools down easier/faster than humid). air temperature during testing 80F (4% relative humidity). block of ice lasted 5 hours (larger blocks can last up to 10). to run the cooler 100% off-grid check out my solar ice making/freezer vids.

# Ice Stand Corrected

This one’s great. Makes perfect sense, it was a new tip for me. I was using ice trays the wrong way, now I know.

Spread the word, we need more ice on 4th of July weekend.

Re-blogged from Foodhack:

In fact, not only does hot water chill quicker, many people think it produces a better quality ice cube. And while ice is an afterthought for most folks, people who are serious about their beverages, alcoholic and otherwise, know that ice matters. After all, as it melts, it flavors what you’re drinking, whether said beverage is vodka or water.

A high-quality “boiled” ice cube vs. a regular “cold water” ice cube. Amazing, right?

Image by isr_Raviv/Instructables

Thanks to Burner Danceburgh AfterDark, who breaks it down in simple terms for us:

it’s got to be pretty hot water, up around boiling temp, near 200 when your average household water temp sis more in the 130-140 range. ANd you lose some to evaporation, which evaporates and condenses all over your freezer …

Back to the Foodhack story:

## How Does This Even Work?

The phenomenon of hot water turning into ice faster than cold water is known as the Mpemba effect, named after a Tanzanian student who observed his hot ice cream mix freezing more rapidly than the cold version.

Separating homemade ice cream into ice cube trays also speeds up freezing.

Image by J. Kenji Lopez-Alt/Serious Eats

recent study by Xi Zhang, Zengsheng Ma, and Chang Q Sun at Nanyang Technological University, Singapore, helps shine some light on a possible reason why this phenomenon occurs.

A water molecule is made up of two hydrogen atoms and one oxygen atom which are bound together by the sharing of electrons, known as a covalent bond. Water molecules are then connected to each other by intermolecular forces known as hydrogen bonds, which happens when a hydrogen atom from one water molecule is near an oxygen atom from another.

H2O: Just one big happy family.

Image via Lightbulb Books

As you can see from the above illustration, the three atoms together form an angle. A hydrogen bond is the result of this structure and is responsible for giving water its unique life-giving properties and its ability to expand when frozen.

According to the Nanyang study, these bonds are behind the Mpemba effect, when hydrogen bonds do their job and bring water molecules into close contact. However, the molecules have a natural repulsion to one another. This action by the hydrogen bonds makes the covalent bonds move apart and store energy.

As liquid is heated, the hydrogen bonds stretch and water molecules are forced to be farther apart. Correspondingly, the covalent bonds within the water atoms shrink and lose energy. This process is akin to cooling off.

On a molecular level, this water is already cooled off. Seriously.

Image via The Dabblist

Essentially, hot water already closely resembles cool water on a molecular level. The energy in hot water is wound up so tightly that when it is released, it cools and freezes faster than cold water.

## How Much Faster Does Hot Water Freeze?

It’s hard to say. Water reaches its freezing point at 0° C (32° F), but the time it takes reach this point may vary. It’s difficult to estimate how much faster ice cubes will form with hot water because many variables must be considered—the initial temperature of the water, the volume of water, and the temperature of the freezer.

Where’s Iceman when you need him?

Image via Tim Graves

Regardless, heating filtered water to a boil will definitely speed up the freezing process. Some even say that hot water makes for cleaner and clearer ice cubes, while others swear by using ice coolers or various methods other than using hot water (including the slow freeze and DIY ice cube trays inside an insulated cooler).

One thing is clear: if you want your ice cubes sooner rather than later, throw it in the freezer as soon as you can pour it into the containers without melting the plastic.

If you live somewhere exceptionally chilly, you can just throw the boiling water off your balcony like these guys.

While you may not be able to instantaneously freeze water, you can perform an at-home experiment with two separate ice trays, and try this method out with cool and hot water. The worst thing that can happen is that you have two trays of ice cubes ready to be utilized.

Just a couple words of caution when using hot water for ice cubes—use BPA-free plastic trays, stainless steel, or silicone ones. Studies have shown that hot water can cause BPA leaching in certain plastics not rated as BPA-free.

Nikola Bregovic

Thanks Mpemba. The Royal Society had a competition to explain the effect, which 22,000 scientists entered. It was won by Nikola Bregovic of Zagreb, the capital of Croatia.

The history of the Mpemba, in fact, goes out the back of Bacon. That’s right Burners. Happy fourth.

http://www.rsc.org/mpemba-competition/mpemba-competition-history.asp

### From Aristotle to Mpemba

The phenomenon by which, under certain conditions, hot water freezes faster than cold water has been observed by some of the world’s finest minds, and has been used in everyday life for centuries.

In the 4th Century BC, Aristotle observed that “The fact that the water has previously been warmed contributes to it’s freezing quickly: for so it cools sooner. Hence many people, when they want to cool water quickly, begin by putting it in the sun”.

Roger Bacon in the 13th Century  used the effect to advocate the scientific method in his Opus Majus, while in his 1620 Novum Organum, Francis Bacon wrote that “slightly tepid water freezes more easily than that which is utterly cold”. Rene Descartes also tried to solve the problem in 1637 and through the years, many scientists have attempted to explain it with little success.

Erasto Mpemba

In 1963, the question was catapulted back into the public eye when a young Tanzanian boy called Erasto Mpemba noticed that if he put hot ice-cream mix into the freezer, it froze more quickly than the cooled ice-cream mix of his fellow classmates.

Mpemba’s tenacity in the face of his teacher’s initial dismissal of his observations and the ridicule of his classmates prompted him to repeat the experiment with hot and cold water, and to stand up and ask visiting physics lecturer Denis Osborne about the phenomenon.

In 1969, Mpemba and Osborne published a paper together (See “Cool?” in the box below), and the effect became known as The Mpemba Effect. In August 2012 Osborne had the following to say about his work with Mpemba:

“In line with his question made in front of his school staff and peers, we tested and found that hot water in Pyrex beakers on polystyrene foam in a domestic freezer froze before cooler samples. We attributed this to convection creating a continuing hot top, noting that:

1. If two systems are cooled, the water that starts hotter may freeze first, but we did not look for ice and measured the time as that until a thermocouple in the water read 0°C.
2. A graph of ‘time to start freezing’ against initial temperature showed that the water starting at about 26°C took longest to freeze (water starting at 60°C took twice as long as water starting at 90°C).
3. Thermocouples near top and bottom showed a temperature gradient in the water. A hot starter kept a hot top while its lower levels were cooler than for the cool starter.
4. An oil film on the water surface delayed freezing for several hours, suggesting that without this film, most of the heat escaped from the top surface.
5. Changes in volume due to evaporation were small; the latent heat of vaporization for all the water to cool to 0°C and start freezing accounted for less than 30% of the cooling.
6. We used recently boiled water for all the trials, making dissolved air an unlikely factor.

We failed to check and report the ambient temperature in the freezer or its consistency during cooling. Lower ambient air temperatures might increase heat loss rates from the top surface, cause more rapid convection and increase the difference in freezing times.

Different mechanisms may assume more importance in different situations. We gave one example, with Mpemba’s initial discovery in mind, and we wrote: ‘rapid cooling of a system that starts hot may be accelerated if it establishes thermal contact with the case of the freezer cabinet through melting the layer of ice and frost on which it rests’.”

Happy 4th of July to all Burners around the world