Math types: Empty milk jugs as emergency flotation devices

Factual Questions
1

I’ve heard emergency rescue experts comment after drownings that should someone in the future be flailing in a pond and rescuers aren’t present to reach him/her, that an empty gallon milk jug can be used as a life preserver until help arrives.

How much buoyancy (displacement?) does an empty and sealed one-gallon milk jug provide? How many would be needed to keep a tired 200-pound man afloat until help arrives? (I’m not even sure how much he would weigh in water.)

My guess is four empty jugs tied together would probably keep him above water.

Close?

2

One. Bear in mind that that tired 200 pound man will ordinarily float with the water line about at his eyes. Adding the flotation of a single gallon bottle will raise his nose out of water.

Plus, more to the point, giving him something obviously bouyant to hold onto will get him to calm the heck down and relax, which is killing him faster than his inability to swim is.

3

The mass of the jug and air inside is probagly negligible in this case so figure that the just will displace about a gallon of water or slightly less as the air might compress slightly when it’s pulled under. A little more than eight pounds.

4

Hmmmm.

So far, we have two answers:

  1. Ethilrist says 1 jug will support the weight of a drowning man enough so that he will not, um, drown.
  2. **Padeye{/B] seems to suggest it would take MANY jugs (8 pounds flotation each for a 200-pound man).

Let’s assume the man has no power to tread water. OKAY, NOW HOW MANY EMPTY PLASTIC JUGS?

5

No, Squire, you’re just getting confused because you asked two similar-sounding but only peripherally related questions, and the responders each picked a different one. The answers to the questions as given are:
“How much buoyancy (displacement?) does an empty and sealed one-gallon milk jug provide?”

About eight pounds, if it is fully submerged.

“How many would be needed to keep a tired 200-pound man afloat until help arrives?”

One.

Huh? Humans are made mostly of water, which exactly displaces an equal amount of water and therefore ‘weighs’ nothing when submerged. Your bones are somewhat denser, but your lungs are much less dense (when they are filled with air instead of with water-i.e. when you haven’t already drowned). Whether or not a man can tread water, he will float in water without effort (unless he is unusually lean, in which case he may sink very slowly) with a lungful of air. Trouble is, unless the very tiny part of your body that will protrude from the surface in this case happens to include your mouth and nose, your lungs will not remain full of air for very long.

Babbling on a little much-the upshot is, you’d need about 25 empty milk jugs to make a raft that could completely raise a 200 pound man out of the water & keep him dry. We’re not interested in that-we want to keep just his head out of the water. One milk jug is plenty to do that.

6

Assuming the big man does not sink to the bottom but in fact floats in water. Which is not a stretch at all since most people float, just not with their mouths above water. What is our objective here? do we want a raft for him to sit on? If so you need at least 25 jugs to support 200 pounds. Keep his head above water? I would guess that a human head does not weigh more than 16 pounds so 2 jugs would do from a buoyancy standpoint. Hold a jug under each are should keep you head above water.

7

Well, milk jugs are plastic and compressable. Buoyancy is simply a matter of displacing water with something that, taken as a whole, is less dense than water.

But, since air-filled plastic jugs are compressable, any attempt at serious buoyancy will result in some crushed jugs. This will, undoubtedly, cause some practical problems.

8

I don’t think the milk jugs will compress much if you don’t force them too far underwater. There is a lot less pressure on the jug if it is just barley covered by water verses three feet under water.

9

SCIENCE MARCHES ON…

Math not being my forte I went the experimental route. (sorta) One jug works.

I did this last summer with a gallon jug of bleach and it helped me float quite well. Two would not haved worked as well unless they were tied together as i had to use both arms to hold the jug.

My question: If you are trapped in the water what are you doing with an empty jug of milk? Or if someone is there to toss you one Why can’t they save you in a more efficient manner?

d

10

That’s exactly what I was wondering, DAMAAN! Maybe you’re just hanging around at a really polluted lake, you start to drown, and just grab whatever piece of garbage floats your way, and LUCKY YOU! It’s a one-gallon milk jug! WOOHOO!!

Seriously, though…um…well, I have nothing to add.

11

re: Q: “Why can’t they save you in a more efficient manner?”

I think the emergency rescue guys were referring to folks who cannot swim well. The idea was to provide some type of emergency assistance. After the drowning of a teenager, the paramedics suggested people carry an empty milk carton in the trunks of their cars, just in case.

SCSimmons, yep, I realized I was asking two questions–and I knew that a person would float fairly well. That said, I had no idea one jug would do the trick. Seems a struggling person would need more, just to soothe them. (Amazing how many lives could be saved with a discarded milk jug…)

Another question: how can an inflated car tire mounted on a wheel provide sufficient flotation? Seems the tire and wheel together would outweigh the air inside. (BTW, I mention this because the same paramedic suggested using a car tire as a rescue flotation device, if nothing else is available.)

12

Just how far can you toss a 1 gal milk jug? It’s so light and has so much air resistance, I bet you couldn’t toss it 15 feet. Someone go do this experiment and let us know the results. I bet you could throw it farther if you added some weight. Hey, I know, fill it with water and toss it to em!

13

I was wondering how to toss it too. and if you could toss it - why not toss a rope? and how many of us are carring around spare milk jugs (and if they are put their for that purpose why not put a rope instead?)

perhaps you have to put some water in it to allow you to throw it.

but as pointed out (and for reasons stated above) the answer is one jug will do it.

14

FTR, empty two-liter bottles are damn near indestructable (until the sun turns them brittle) and can be bound together to make a good raft.

15

Would a jug filled with oil or petrol also work?Obviously,oils are far more dense than air,but this would also overcome the practical problem of tossing it a long distance.So the question in this case again,how many jugs of petrol for a 200 pound man to keep his head afloat?

Heck,one might as well buy a lifebuoy and carry it around.

16

It won’t work very well at all, because gasoline has a specific gravity about 0.7-0.8 of water, so you’re not going to get very much buoyancy. Hell, some oils are heavier than water - Orimulsion has a specific gravity of about… 1.13, IIRC. So it would drag you down with it somewhat.

17

Because you might not have a rope.
[WARNING: TANGENT]

REACH,
THROW,
ROW,
GO,
in that order

Keep as much distance between a drowning person and yourself. A drowning person will desperately try to climb onto anything that comes close, including anyone trying to rescue them, which could leave the authorities with two bodies to pull out of the water instead of one

Reach: If a person is drowning close to the bank, lay down and reach for them with an arm or leg, but keep your balance when reaching to them. Don’t let them pull you in.

Throw: If you can’t reach them, then try to throw anything nearby that floats or can pull them in: milk jugs, ropes, tires …whatever. If you have an empty milk jug, use it!

FWIW, my father almost drowned at the beach when he was a kid; the one thing he remembered of the day was a line of fishermen standing on the shore, well within casting range, staring and holding their poles.

Row: If you have a boat or raft available and can’t throw something to them, then go out and try to get them. This is a next to last resort because it takes time and a drowning person could capsize a small boat.

Go: Swimming out to the person should be a last resort and only tried by people who have received water safety training.

If someone is drowning, all you have is a milk jug and they are too far away for you to throw the jug to them, then you might swim out until you are about 5-10 feet away and then throw the jug the last few feet. DO NOT get within arms length for any reason. If they do somehow grab you, dive and get away.

Sorry for the long winded tangent, but this is sort of a personal thing with me. I hope I wasn’t completely inappropriate to post this here.

18

Thanks for helping me look more reasonable, Cornflakes.

FTR, I almost drowned several years ago when attempting to rescue a drowning man. I went in the water reluctantly–filled with terror, actually–considering my mediocre swimming skills and non-existent training. He was in Total Panic Mode and, when I reached him, he pulled me underwater several times. I tried to fight him off but, being tired from the swim, could not. He was going absolutely crazy and soon we both were underwater and drowning. To this day, the sketchy, black memories of my almost drowning are still terrifying and every few months I have these horrifying “night terrors,” as my physician calls them.

Fortunately, for both of us, two off-duty Navy guys (special force SEALS, according to news reports) were came to our rescue. Though I don’t remember the incident, as I was unconscious and underwater, if not for their heroism, we both would have died. The incident made the local evening news that night, at which time an interviewed paramedic pointed out to viewers that inside a nearby trash bin he found an empty gallon container of fruit juice that could have been used as a flotation device.

Turns out the other guy had been drinking.

Cornflakes, you’re absolutely correct about everything you say. To the rest of you–be prepared.

You fatigue very quickly in water–and panic soon thereafter.

19

Glad I helped, Country Squire. Nothing can stir up a tangent-fest like a request for objective information about an emotionally hot topic

If I did the math right, a gallon jug filled with air will provide 8.34 pounds of buoyancy. The US Coast Guard requires that a Type II PFD have at least 15.5 pounds of buoyancy (PFD–personal flotation device; Type IIs are the horseshoe type life jackets.) A gallon jug is halfway to the buoyancy of a proper life jacket. It probably also has a psychological benefit in that it gives the victim something to cling to. After all, people float when they lay still in the water. A drowning person will probably be better off if they can cling onto something floating and settle down.

20

funny - I have been around and in the water all my life. from scuba in extreme currents through a boulder field to running out of air off shore w/ the current against me to fallen through the ice in the winter - never once in my life did I think I was going to drown.

I guess this is another tangent.