Hydrogen Balloon Explosions Rubin Battino' and Benjamin S. Battino Wright State University, Dayton, OH 45435 Pirketta Scharlin University of Turku, SF 20500 Turku, Finland
Hvdroeen balloon explosions are amone the most popular ;hemysty demonstr&ions. They are dramatic and kiorful(11and loud. After the senior author attended a searion at ChemEd '91 where the presenters exploded a dozen balloons filled with a HdOz mixture in a mid-size lecture hall, wore ear protection themselves, yet neither cautioned the audience about the loudness of the explosions nor gave any instructions about how the audience should protect their ears, Battino and his wlleagues felt compelled to write this article. When his ears stopped ringing, Battino wondered about the sound levels and planned the series of experiments reported here concerning the loudness of different size balloons in various room sizes and as a function of distance from the explosion. Hflz mixtures also were tested. Caution: Regarding Your Hearing lf you do not have proper ear protection, cup your hands in front of your ears. Covering your ears with your hands is not as effective The sewnd motivation for this paper . . arose from a telephone conversation the senior author had with an *expert" who manned a local "balloon store." We wanted to find out how balloons were sized and what sizes were available. (Balloons are sized by their expanded diameter in inches popular sizes are 5, 7, 9, 11, and 13 in.) Most balloons are made from latex rubber. The salesman surmised that balloons filled with helium shrank in size after about eight hours due to the length of time it took for a "chemical" reaction between the helium and mbber to take effect. After we offered to guide the salesman to a Nobel Prize if he could prove this, he started hedging! This exchange gave rise to the second set of experiments (which we will report on first). How does the size of a balloon change with time when it is fdled with Hz, He, CH4, and N2 (for comparison)? Diffusion and Gas-Filled Balloons
Four different-sized latex balloons 7, 9, 11 in., and "Krazy Kat" which had an odd shape with a maximum 13in. width were fined with He, Hz, and CH4. (At the end of this section we report on results with Nz and Mylar foil balloons.) Our machine shop fabricated a set of calipers from a roofing square, and measurements were made of the maximum diameter in inches to 1/16 in. as a function of time. The He and Hz measurements were over a time period of about 95 h, and those for CH4 about 165 h. The results for these measurements are given in Table 1 as parameters fmm a least-squares fit of the data to the equation Dlcm = A (th)+ B
where D is the diameter and t is the time. In almost all cases, the correlation coefficient was 0.99 or greater. The decrease in size is linear for about the first 10 hours and the coefficientsin Table 1are for this time period. Aleast'Author to whom correspondence should be addressed.
Table 1. Coefficients in the Equation Dlcm = A(Uh) + B for Diffusion of Gases Through Latex Ballons
Balloon Size (in)
Hydrogen A
B
Helium A
Methane A
B
B
KKa -0.461 KKa 4.416 K K ~
30.69 28.71
4.368 4.280 4.274
32.94 31.17 31.62
-0.121 -0.130
4.463 4.496
17.70 18.44
-0.551 -0.517 -0.327
19.11 20.39 21.62
4.0997 17.64 4.110 16.93
7 7 7
Ave.
-0.53
4.37
28.80 30.85
4.13
"'Krazy Kat'balloon, W i n , maximum.
squares fit for a 95 h run on an ll-in. balloon filled with He required a quartic for an adequate fit. There is an obvious continuous decrease in size which means, alas, no Nobel Prize for the balloon salesman! Not surprisingly, the Hzfilled balloons decrease in size faster than He which is much faster than CH4.The table also contains average values for the "A" term. The ratios of the square roots of the molecular weights are roughly equal to the ratios of the respective A values. An exact correspondence is not expected due to differing surface areas of the balloons. (This, of course, might be a good experiment for someone to try,) We reused some 7-, 9-, and ll-in. balloons with He to test whether a prior stretching had any effect on the diffusion rate. The average Avalue of 0.415 is within the variations to be expected. We tested Mylar foil balloons with He along with 7-, 9-, and ll-in. balloons fdled with Nz as a control. Over a period of three days we found no decrease in size for the Hemylar foil or Nz/latexballoons. There were minor variations due to fluctuations in room temperature. The Mylar foil is an effective barrier to He diffusion, but these balloons are also significantly more expensive than the latex ones. Loudness of Hydrogen Balloon Explosions
Before discussing the' results of our experiments on the loudness of hydrogen balloon explosions, it will be useful to review how loudness is measured and to wnsider OSHA (Occupational Safety and Health Administration) standards. Sound pressure levels (SPL) are measured in decibels (dB) given by Volume 69 Number 11 November 1992
921
dB = 20 log,, (PIP&) where P is the measured pressure and PEfis the standard reference pressure of 20 pNImz. So, sound intensity is actuallv measured on a loearithmic scale relative to a referencr pressure and is basically a pressure measurement. The noise level of zero d H is the startine ooint of the scale that can he and PEfwas chosen as the "weakest &d heard by a person with extremely good hearing in a quiet location." (Olishifski (2)gives background information on noise measurement and levels.) Table 2 gives the OSHA (3) standards or permissible noise exposures on what is called the "A" or slow response scale.
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Table 2. OSHA Permissible Noise Exposures (4)
We used a sound level meter that recorded maximum sound levels. Balloons were filled with Hz gas to measured diameters using our giant calipers. They were tethered about 2.5 m above the floor. Results are given in Table 4 and are the average of measurements done in triplicate. The average of all of the average deviations was 1.7 dB(A) with a range of 0.4-4.2 in the average deviation. Also given in the table are the approximate rwm volumes for very large and large lecture halls, and an ordinary size classroom. Mixtures of approximately 2:l ratio for HzDz also were tested using smaller balloons. As you would expect, for any given distance the sound level (actually a pressure!) generally increased with increase in balloon size for all of the rooms. However, we were able to demonstrate that beyond a certain size (13 in.) that the sound level actually decreases. For Hz to burn, it must come into contact with the Oz in the air. Once a balloon bursts and the H2 is ignited it takes a finite time for the two gases to diffuse toward each other to react. The larger the balloon, the longer this takes, and this is indicated by the sound levels. We have exploded very large (up to 36 in. diam.) balloons with no apparent increase in sound level. (You might recall seeing movies of the burning of the Hindenburg which was not an "instantaneous" explosion.) CAUTION: Regarding Ballwn Size and Thickness
Noise Level References in an office 5&60 dB cluse ta a power lawn mower 90 dB in a woodworking shop 110 dB 100 ft from a 50 hp siren 120 dB a jet plane overhead 140 dB 'near a rocket launching pad 180 dB
Attemotine to ienite a thick rubber balloon can result in meily Gwning a hole in the halloon horn which Hz hoots out in a dnngcrous, large burningjet. HJ02 mixtures explode with extremely loud noises and impact because there is effectively no waiting time for the 0, in the air to diffuse into the Hz.Ceiling panels can be hocked out with large balloons. We recommend using the very smallest HJOz balloons for demonstrations. The smallest ones of 5-7 in. diameter are sometimes heavier than air and should be suspended from a rod on a ringstand.
Asound level of 140 dB is considered to cause pain, a n d exposure t o impulsive o r impact noise should not exceed 140 dB peak sound pressure level. CAUTION: Regarding Decibel Leuels It is generally considered that any exposure of unprotected ears to sound levels greater than 115dB(A) is hazardous and should be avoided. In Table 3 are given acceptable exposures in terms of the number of exposures per day. For example, it is permissible to be exposed 7 times to a 140 dB(A) noise if the duration of each noise were 0.517 min or about 4 s each. A single exposure to 128 dB(A) for 0.5 min has the same impact. The loudest noise we measured was at 10 m for an 11in H2/Ozballoon and was 128.7 dB(A). We should note that the ACGIH (American Conference of GovernmentalIndustrial Hygienists) standards for exposure to noise are onehalf those of OSHA (4).
We mentioned earlier that we tested diffusion for He through Mylar foil balloons. We also have tested exploding Hz-filled Mylar foil balloons. Table 4. Sound Levels in dB(A) for HrFilled Balloons Dist(m) 6in.
5
3
11 in. 13in. 15in. 17in.
99.3 103.5 108.5 103.8
10
96.2 103.5 108.5 102.9 106.5
15
94.6 102.0 104.9 100.8
10
7
-
122.0' 128.7a
Room Volume
Number of Occurrences per Day 1
gin.
Room Volume 2670 m3
Table 3. Acceptable Exposures in dB (A) to Noise a s a Number of Occurrences per Day
DailyDuration (min)
7in.
760 m3
3
104.0
108.4 109.9 112.1
111.3~
6
106.7
106.5 110.0 109.6
111.6~
9
103.4
104.8 107.2 110.4 1 0 8 . 6 ~
124.5'
126.7a
6
113.5'
Room Volume = 210 m3 5 VOl
(L) =
102.4 1.85
2.94
101.8 107.8 6.25
11.42 18.85 28.96 42.15
s R ~ u g h l y2:1 mixture of Hz and 02 by volume '"~razyKat" balloons. Maximum diameter = 13 in.
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Journal of Chemical Education
CAUTION:Regarding Mylar Foil Balloons Do not try to explode Hz-filled Mylar foil balloons. They do not explode, the foil burns, slowly settles, and constitutes a serious fire hazard. Some Final Comments
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Hvdmeen balloon exdosions are verv r with "o.o ~ u l a and information we have given in this paper, you the should be able to use them in a way that protects the audience's hearing. You need t o b e very careful with baumns. Use the size praethe size of ticable.
Acknowledgment PS admowledges the support of the Maj and Tor Nessling Foundation, Finland. We also appreciate the assistance given us by T. Dearhaugh of our Environmental Health and Safety Office and G. Wiles and J. Arehart of our machine shop. Literature Cited
&
1- Fortman, J.J. J Chom Educ. 1891.68.931-958. 2. Olishifah, JB.,Ed. Tundamentala of Indushial Hmiene.. 2nd ed.,National Safety Council,Chicago, 1979. Also,eeeBeauEeu,H.H. and Buehan,R. M. %antitative I ~ ~ U B ~~ ~ ~ S IgG i ~~STPM ~ ~R ~~X S I:N; ~ W~~Y O ~1981. ~~ , ~ 3. OSHA. Seetion 1910.95: 'Oeeupationsl Noise Exposure,' 1974. A h , see "TL\rs, Threshold Limit Values, far Chemical Substances in Warhmam Au Adapted by ACGM for I!%o."
Volume 69 Number 11
November 1992
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