A Comprehensive Guide to Pumpkin Drop

Tom Quetchenbach, 2006-11-01

[top] Table of contents

• Spoiler warning
• Pumpkin drop history
• Getting pumpkins
• Other stuff to get
• Talking to people
• Funding
• Before the day of the drop
• On the day of the drop
• Freezing procedure
• The night of the drop
• Electronics
• APPENDIX 1: Safety Office guidelines
  • Fire Safety
  • Fall Protection
  • Spectator Safety
• APPENDIX 2: Assorted communications with Dan O'Hanlon

[top] Spoiler warning

Pumpkin Drop really only has one surprise. This page reveals it. If you haven't seen a pumpkin drop before, and you plan to go sometime, you may want to remove the spoilers.

[top] Pumpkin drop history

The first pumpkin drop seems to have been in 1972. For some history of the pumpkin drop, see here.

[top] Getting pumpkins

In 2006, pumpkins were $2.99 at Smart & Final and Trader Joe's. You'll need a lot. We had about 16 medium to large pumpkins and a bunch of tiny ones; having a few more large ones might be good. It's nice to have one or two really big ones. Make sure they fit in the coolers.

You'll need some unfrozen pumpkins as well: three or four for jack-o-lanterns and one for the head of the dummy, plus possibly others for other purposes.

There's a pumpkin patch on Foothill and San Gabriel or something like that. We went there in 2005 and they were a lot more expensive.

We bought five 96-quart styrofoam coolers at Smart & Final. They might not sell them anymore. I had to call several stores before I found one that had them.

I had to buy two pumpkins on the day of the drop. Finding pumpkins on Halloween, especially if you don't have a car, is a bit tricky; I ended up going to Wild Oats, where two medium pumpkins cost $7.

[top] Other stuff to get

• Denatured alcohol and boric acid to make green fire. You can get these at Home Depot. If you don't have a car, you can bike to Pasadena Hardware & Plumbing, which is on Fair Oaks just north of the freeway, but be sure to bring a backpack for the denatured alcohol. Boric acid is commonly used in roach poison, such as Copperbrite Roach Prufe.

  You probably want two gallons of alcohol.

• Glowsticks: I don't know the best place to get these. I got them from a Halloween Super Outlet store, but they were expensive ($2.99 each). You may be able to get some from housing (but only one color), as they're used for emergency lighting and have to be replaced every year. (We did this for Drop Day one year.) Do something creative with the glowsticks.

• Rope to tie off the ladder (see below)
• Secondary containment devices for ethanol: I bought foil roasters from Pavilions. (This is a Safety Office requirement. After nearly burning down the mods, I have come to the conclusion that it is a reasonable one.)
• Electronics (see below). Also safety pins to attach the LEDs.

[top] Talking to people

Talk to people a couple of weeks before the event. Don't send emails and wait for people to get back to you; just go to their offices and talk to them in person. If you do send emails, make them short and to the point.

Despite all the shit we (sometimes deservedly) give the administration, everybody I talked to was quite helpful and willing to work with me.

The names mentioned here were correct as of 2006. I believe Malina no longer works in the Deans' Office (but somebody there will have the forms), and I don't know about the others.

• First, get an event registration form from Sue C in Campus Life (or from Malina in the Deans' Office.)
• Talk to the dean about liquid nitrogen. You will need five dewars (320 liters each). He'll send an email to Rick Germond at the Central Warehouse. (You may have to remind him of this fact.)
• Talk to Gregg Henderson at the security office above the credit union. He'll need to sign the event registration form.

• Talk to the Safety Office. Someone there (in 2006 it was Art Seiden) may want to go up on the roof and make sure the ladder is tied off. You can also get fire extinguishers from them. They gave me a sheet of paper with the following information:

  • no dropping anything that's on fire
  • if flaming (stationary) jack-o-lanterns are used
    • there needs to be a secondary containment device to catch the ethanol if it spills, inside or outside the pumpkin.
    • fire extinguishers need to be on hand.
    • spectators should be kept clear.
  • The ladder used to access the upper roof should be tied off. (Tie a rope from one of the rungs of the ladder to something strong.)
  • No more than six people on the roof at any time
  • Don't go beyond the guardrails.
  • Spectators need to be 50 feet from the drop zone.

  (In my opinion all of these safeguards are quite reasonable.)

  If you don't understand something that Safety tells you, just ask them to explain it. I had to get Art to explain how to tie off a ladder a couple of times. If you act like you're actually interested in safety they'll be thrilled.

  Safety will need to sign the registration form.

• Talk to the Grounds Department. I went to the grounds office that's in the same building as the gas station in the physical plant area. (The outside door is marked "Grounds Department and Transportation".) They'll put down plastic and provide a dumpster. Delmy Emerson will need to sign your registration form; she's not in the aforementioned office, but they'll be able to tell you where her office is. (She's somewhere in the Campus Planning building, I think.)

• Talk to Rick in the central warehouse (at the same loading dock as Central Receiving in the P-Plant). He'll probably tell you that you need to wait to pick up LN2 until the day you need it, since five dewars is a lot. They'll deliver it for you, but if you want you can save quite a bit of money by hauling it over yourself; they'll provide a hand-truck. Note that 320 liters of liquid nitrogen weighs around 570 pounds (not including the weight of the empty dewar), so you'll want somebody to help you push the hand-truck if you choose not to have them deliver it. You can also get the bent pipe/nozzle thingy that you attach to the dewar from Rick. If you can't get one I've heard (from the moles) that you can use a funnoodle, but be careful.

  Note that the Moles play with liquid nitrogen a lot, so if you have a liquid nitrogen question you should ask them. They're really not so bad, once you get to know them.

• I didn't talk to anybody associated with the library. It might conceivably be a nice thing to do.

[top] Funding

You can get $100 from ASCIT and another $100 from the GSC. See the GSC website: http://www.its.caltech.edu/~gsc/funding/. I used their "quickfunding" process to get money in 2006. They didn't especially like the fact that I was using this for an annual event; if you have time, email a proposal to the GSC budget committee instead. (See the GSC website.)

Note that you can probably get ASCIT funding even if you ask them after the event. This will probably not work with the GSC.

Here is the budget for the 2006 drop:

Pumpkins and coolers	Smart & Final	$169.98
Last minute pumpkins	Wild Oats	$7.00
Batteries and foil pans	Pavilions	$24.31
Rope and pyrotechnics	Pasadena Hardware & Plumbing	$45.42
Glowsticks	Halloween Super Outlet	$38.32
Electronics	EE Stockroom	$28.25
Liquid Nitrogen	Central Warehouse	$207.48
Total		$520.76

[top] Before the day of the drop

• Talk to people (see above)
• Make posters. If you get GSC funding, you need to include the following notice: "All members of the Caltech graduate student community are welcome to attend. Co-sponsored by the Graduate Student Council. Additional funding from Institute Housing and Campus Life." You can use their graphic. The posters should state that pumpkin drop is at 11:59:59 PM on October 31 at Millikan Library. "Millikan" is not spelled "Milikan."

• Choose your roof crew. You can have four people in addition to yourself and a security officer. You'll need to go up on the roof in the daytime, probably the day before but possibly the day of, and show people around. Note that the west side of the roof is shaped like this:

       ^               ______________
       N           __  |
    <W   E>       |  |_|
       S          |    |    1
       V          | 3  |___
                  |    |b  |
                  |   _| 2 |
                  |__|c|a  |L
                       |___|_________
  
    

  Region 1 is the "lower roof," which has high walls around it. Region 2 is the "upper roof", which you reach by climbing the ladder at the point marked L. Region 3 is the side roof where the actual drop takes place. There is a wall between regions 2 and 3 such that from the upper roof you cannot see the point labeled "c" from the point labeled "a" unless you lean over the wall or are somewhat tall. Be sure that everyone understands that climbing over the wall at point "a" is bad. Place a stool at point "b" and insist that everyone who climbs from region 2 to region 3 use the stool. Make no exceptions to this.

  Pumpkins are dropped off the west wall of region 3. This wall is around six feet tall, so you'll probably want something to stand on so that you can see what you're doing. Chairs with legs will damage the foam roof, so use those little step-stools that live in the library.

  Call Security at extension 4701 when you need to get on the roof. They're usually able to send somebody within a half hour of you calling, but it depends on how busy they are.

• If Safety is actually going to inspect the setup, tie off the ladder at point L. Tie a rope between one of the rungs of the ladder and something sturdy; we used a bracket that mounts a large electrical conduit to the wall. The safety people are busy, so do this well in advance if possible. In 2006, somebody moved the ladder between when we tied it off and when Safety came to inspect it, and I had to go up again.
• Get LN2 (see above) and start freezing pumpkins (see below).
• Get fire extinguishers from Safety.
• Find somebody to do music and figure out where we're going to get speakers and an amp. We usually get these from Ricketts.
• Get someone to light the jack-o-lanterns and stay at the bottom with the fire extinguishers. Make sure that this person knows how to use a fire extinguisher.

[top] On the day of the drop

• Carve jack-o-lanterns. Be sure that all holes are high enough on the pumpkin that it can hold a significant amount of alcohol.
• Talk to Security and remind them to put up caution tape 50 feet away from the drop zone. Also ask them if they'll take the coolers and speakers over to Millikan in their van or a cart. Let them know approximately when this will happen.
• Get frosh to build a dummy with an unfrozen pumpkin for a head.
• Make sure that Grounds is putting down plastic.

[top] Freezing procedure

Note: this is how I did it and more or less how Dan O'Hanlon did it before me. You're welcome to change the procedure as you see fit.

If possible, freeze the pumpkins (in a freezer) before you use LN2, or at least get them cold, so that they won't crack as easily when you start using LN2. I got people to volunteer freezer space. We used to use the walk-in freezer in the SAC, but it's unclear whether that will continue to exist in the future.

Start the freezing no more than two days before the drop. Longer than that is just wasting LN2.

For the first few fillings, add LN2 until it's about an inch or two deep in the coolers. A filling seems to take a little less than half of a 320-liter dewar. The first time you fill the coolers, it will all boil off rather quickly, so you may want to refill after a couple of hours. On the day of the drop, increase the depth; after the final dose, you probably want to have LN2 about 5 or 6 inches deep in the coolers.

Insist that everyone who helps you with filling coolers is wearing shoes and long pants. You probably also want to wear gloves and a long-sleeved shirt. You may also need something to use as a "dipstick" to check the depth of LN2 in the coolers; I used a wrench. (You need a wrench anyway to attach the tubing to the dewar.) A flashlight is useful for filling at night.

To keep people from playing with the LN2, store the nozzle/tubing away from the dewars when you're not using it.

I used roughly the following schedule:

10/29	11:00 am
10/29	2:00 pm
10/30	2:00 am
10/30	10:00 am
10/30	5:00 pm
10/31	12:00 midnight
10/31	6:00 am
10/31	12:00 noon (4 inches)
10/31	3:45 pm (4 inches)
10/31	7:30 pm (6 inches)

I probably should have started somewhat later; maybe 2 or 4 PM.

Adjust the amounts that you use based on how much LN2 you have left. Keep in mind that the gauges on many dewars don't work.

If you can smell pumpkin when you open the coolers, it means the pumpkins are not frozen. This is normal for the first few fillings, but if it persists it means you need to fill more often or use more LN2.

On the night of the drop, I had about 5 or 6 inches of LN2 in the coolers, not boiling. That is pretty cold.

[top] The night of the drop

Call security when you're ready to move things over, probably at around 10:30. (We started at around 10 and had a lot of time on the roof.) Right before you call, check the coolers for liquid nitrogen and drain out any that's left by placing the coolers on chairs and poking several holes in the bottoms with a screwdriver or something similar. Be sure that everyone who's standing nearby is wearing shoes and pants. People will probably come and watch, because coolers draining LN2 at night is a pretty impressive sight.

Give the cell phone numbers of your roof crew to your ground crew, and know their numbers. Arrange to have them call you if anything goes wrong. If anyone on the ground crew calls you, stop dropping immediately until you know what's going on.

Once on the roof, call your ground crew and make sure they're ready to start dropping at midnight.

Don't drop all your pumpkins at once, but don't go too slowly or the crowd will get bored. Drop the dummy close to the end. It can be fun to tease the crowd by holding up a pumpkin (especially a blinky one) and then taking it away, but don't do too much of this or they'll get bored. (A good way to end is to hold up an LED pumpkin, take it back, drop a regular pumpkin, hold up the LED pumpkin again, etc. But don't overdo it.)

Once you're done, clean up before the pumpkin chunks thaw.

[top] Electronics

Having some blinking pumpkins may be a good idea. The best way to attach LEDs to frozen pumpkins seems to be to use a strip of duct tape a bit more than 3 feet long. Place about 20 LEDs in the tape and wire them in parallel. If you just want them to light up, you should connect them to a battery through a small resistor. If you use three AA or AAA batteries, you should start at around 51 ohms and try lower values until you get the brightness you want. If the LEDs start emitting the wrong color light, disconnect the battery right away (before the LEDs burn up) and use a larger resistor value.

(I say 51 ohms rather than 50 because the standard resistor values are 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91, and so on.)

We've traditionally used wire-wrap with the idea that the low temperature will crack solder joints. For the LEDs, this is probably true. For the controlling electronics (if you make the lights blink), this is not the case.

If you have time, order bright LEDs from Digi-Key or Mouser. Otherwise you'll have to get them from the EE stockroom, where they are not too expensive but also not too bright. The Digi-Key catalog (and probably the Mouser catalog as well) lists LEDs in tables with intensity in millicandelas. (The candela, in case you're interested, is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 THz and that has a radiant intensity in that direction of 1/683 watt per steradian. Glad I got that cleared up...) Anything over 1000 mcd is pretty bright.

Tim recommends superbrightleds.com. I have used their LEDs for drop day and EE 91; they seem to be a good source of bright LEDs although you may be able to find cheaper ones. They sell a "violet" LED which is really a blue LED with a red phosphor. Their selection is not quite so dizzying as those of Digi-Key and Mouser, so it's easier to find what you want. They sell high-brightness green LEDs that are much less expensive than those from Digi-Key.

The EE stockroom is 029 Moore (the sub-basement). You can pay with your student account. The LEDs are behind the counter on the left. Feel free to just walk behind the counter and start browsing. Don't ask the stockroom clerk (Janet) any questions about the parts; she won't know the answers. Google the part numbers and look at datasheets instead.

You can also try DuVac Electronics on Colorado and Bonnie (east side of PCC), or Radio$hack (north on Lake, near Roscoe's). For general electronics shopping, I also recommend All Electronics. Their store in Van Nuys has everything in their catalog in stock.

You can't put LEDs of different colors in parallel. (Well, sometimes you can, but test it before you do it.) If you need to drive different colors of LEDs from the same source use a separate resistor for each color, like this:

                    |\ | red
   +------/\/\/\-+--| >|----+
   |             |  |/ |    |
   |             |          |
   |             |  |\ | red|
   |             +--| >|----+
   |             |  |/ |    |
   |             |          |
   |             |  |\ | red|
   |             +--| >|----+
   |                |/ |    |
   |                        |
   |                |\ | grn|
   +------/\/\/\-+--| >|----+
   |             |  |/ |    |
   |             |          |
   |             |  |\ | grn|
   | +           +--| >|----+
 -----           |  |/ |    |
  ---            |          |
 -----           |  |\ | grn|
  ---            +--| >|----+
   | -              |/ |    |
   |                        |
   +------------------------+

Sometimes this is true even for different kinds of LEDs that are the same color. The reason is that different LEDs have different forward voltages; for example, red LEDs are usually 1.7 volts and green ones are usually 2.1 or 2.4 volts. Assuming low resistance wires, the voltage across several LEDs in parallel will be close to the minimum of the forward "on" voltages of all the LEDs, so only those LEDs which turn on at that voltage will light up.

Even the above circuit diagram is poor design; because of manufacturing tolerances, resistance in the connections, etc, every LED should really have its own resistor. If you use thin enough wires (like 30-gauge wire-wrap wire) you will probably see that the LEDs closer to the batteries are brighter. But for something that nobody's going to see up close and that's going to be dropped off a roof, you don't need to use the best design practices.

If you want blinky lights, find a EE or something. Or, if you know something of electronics, look at my heavily annotated schematics for simple blinky lights in PDF, PostScript (gzipped), or gschem format.

Be sure that there are two strips of duct tape per pumpkin, even if one doesn't have any LEDs on it, so that the assembly doesn't fall off the pumpkin on the way down. Attach them with safety pins. If you do this early enough you can test with an actual pumpkin.

[top] APPENDIX 1: Safety Office guidelines

Fire Safety

The students would like to coat pumpkins with ethanol and ignite them for a "Flaming pumpkin drop". "Flaming Pumpkins" should not be used during this event due to the inherent risks involved For both spectators, and event participants. The Institute Fire Policy specifically states:

[OCR + italics + official policy = fun]

_ "Flammahle li'gui'ds, gases, soli'ds, andexplosi'ves, i'ncl_djng_ìrewor_, mup_, not bepossessed oy wsed oM IMsti'tuteproyer_ _cept i'n approved campws locuti'ons wnder rhe uwthorjJy ofrhefurulr}Jfor reasons ofacademi_c reseurch, - __(PICTURE)._(?horato_, or teachi'ng acti'vi'ti'es.''

The decorations for the event involve two stationary jack-o-lanterns that will be lit using ethanol. The Safety Office recommends that this process be replaced by a less hazardous altemative if possible. If ethanol is to be used the following are recommended:

• A secondary containment device designed to contain the alcohol if it shoud spill from the pumpkin (this containment can either be placed inside the jack-o-lantern or the jack-o-lantern can be placed in a containment tray).
• Fire Extinguishers on hand to extinguish the jack-o-lanterns in the event of a problem (Extinguishers will be provided by the Safety Office the Friday before the event)
• Spectators should be kept clear of the jack-o-lanterns

Fall Protection

Because the event will involve individuals on the roof of Millikan library, the following shouId be done to prevent a fall hazard:

• The ladder used to access the upper roof shouId be tied off
• Roof access should be limited to those involved with the drop. There should be no more than 6 people on the roof at any time.
• Individuals involved in the drop are not to go beyond the guardrails.

Spectator Safety

Because of the potential for pumpkins missing the mark, spectators need to be kept at a safe distance (at least 50') from the drop zone.

It is the student's responsibility to contact all other departments that may need to be involved with this event, including but not limited to: Physical Plant, Grounds, Security, the Library, and Student Affairs. If there are any questions regarding the safety issues for this event please contact the Safety Office at extension 6727.

[top] APPENDIX 2: Assorted communications with Dan O'Hanlon

Date: Sat, 14 Oct 2006 00:11:16 -0500
From: "Daniel O'Hanlon" <xxxxxxxxx>
To: "Tom Quetchenbach" <xxxxxxxxx>
Subject: Re: pumpkin drop

Grad School is great.

Pumpkin drop:

People you need to talk to:
Safety (because they like knowing things)
Security (for roof access, pumpkin transport, and caution tape)
Dean Hall (for LN2)
Grouds (for plastic and dumpsters)
P-Plant (to order LN2, can use UID to order)

The styrofoam coolers we used last year were the best ever.  Get the
same kind if you can.  figure out some way to get the pumpkins cold if
not freezing before you add LN2.  This will reduce
cracking/shattering.  The coffee house freezer was the best.  Good
luck finding freezer space.  The green fire was made by adding boric
acid to ethanol.  Boric Acid is 99% of roach poison.  Just buy some at
home depot.

Talking to people sooner is better.

Take people up to see the roof in the daylight.

Email me if you have any more questions or call me at xxx-xxx-xxxx

~DanO

virtualphtn: hey
DanO: hey
DanO: sorry, I forgot to reply earlier
virtualphtn: no problem
DanO: I believe I got five last year
DanO: it was enough
virtualphtn: ok, i'll do that then
DanO: four, my sophomore year was not enough
DanO: Also...
DanO: I'm thinking that starting to freeze them more than two days beforehand is unnecessary
DanO: you mostly just have to have them below freezing temp
virtualphtn: how early did we start last year?
DanO: then when you start adding LN2, don't let them go above
DanO: We started about 2.7 days before
virtualphtn: that seemed to work pretty well
DanO: it would have been better if we had started later
DanO: it worked fine
DanO: but the first day or so was useless
DanO: because they thawed over the first night
DanO: so it mostly was just a waste of LN2
DanO: I recommend a moderately linear increase of LN2 with each dose
DanO: so that when you finally have security come to get them, you have to pour the excess off
DanO: because although it was annoying
DanO: it was perfect
virtualphtn: how much (roughly) do you use?
virtualphtn: (for one filling, I mean)
DanO: About two inches at the start
DanO: between 6 and 8 by the end
virtualphtn: all right
DanO: it would also be better if you found a place to do them inside
virtualphtn: yeah, unlikely
DanO: indeed
virtualphtn: maybe we can get rid of some of the junk in the sex trailer, but probably not in time
DanO: I don't think the sex trailer is the best idea
DanO: anywho, don't worry about it
DanO: just find people to do music, the dummy, jackolanterns, posters, LEDs, etc...
DanO: and try to do something new too if you can
virtualphtn: yeah, if i can think of something
virtualphtn: that doesn't involve something stupid, like dropping things that are on fire
DanO: yeah, safety won't go for that
virtualphtn: do i need to actually fill out an event registration form, or should i just talk to the appropriate people
virtualphtn: ?
DanO: fill it out to be safe
DanO: security will like it
virtualphtn: yeah, that's what i figured
virtualphtn: one other thing...is roof crew usually four or five people?
DanO: five
DanO: plus one guard
DanO: I don't think they let more up there
virtualphtn: ok
virtualphtn: well, I've got to go do EE stuff...thanks for the help :-)
DanO: cool
DanO: adios
DanO has become idle.
DanO is no longer idle.

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