“MYTHBUSTERS”: GAS EXPLOSION IN THE ROOM

In this episode of popular scientific program “Mythbusters”, shown on Discovery Channel, Jamie Hyneman and Adam Savage who are experts in special-effects are experimentally testing to the limit the legend from movie about Borne.

Spy thrillers about Jameson Borne filmed according to Robert Landpam’s books tell about adventures of the former employee of CIA, they are about professional killer who lost his memory. These movies were high in the ratings and also were the winners of Oscar awards.

The busters put their hands to the myth from “The Bourne Supremacy” episode. There you can see the scene where Borne gets to an apartment and, knowing that he is chased by bad guys, he breaks gas valve to allow it fulfill all the room. Then Borne puts a magazine to the toaster, turns it on (organizing a “detonator with delay”) and leaves the house. In 20-30 seconds when the magazine inflamed, explosion happens breaking the windows. Borne escaped his chasers, winning the next battle with the smart. That should be expected. But is this effect possible in real life? Can gas leak together with magazine forgotten in the toaster blow up a room?

Myths, rumours and cinematography provoke our unconscious fears of potential danger concluded in the power of liquefied fuel. This fear and fallacies about independent gasification frighten people away. Secure gas use is put in doubt in spite of the fact that beginning from 1952 there have not been detected any accidents in the world connected with independent gasification. Gas as an explosion cause is a tired stereotype. Only the fire inside the house might pose the threat.

To provoke an explosion there are three conditions are required: closed space, fatal concentration limit of the gas in the air and fire resource (spark).

We can see three components of “Borne’s escape”: toaster, magazine and natural gas. First of all the experts of the program cleared up if a magazine can flash from the toaster and how fast this inflammation can occur. As a result of this experiment there was found the most appropriate magazine (inflammation time – more than 2 minutes).

Then Adam and Jamie continued with the examination of the next part of the legend – methane. Methane is the natural gas which is used in the kitchen for cooking. Encyclopedia says: “Methane (CH4) is the elementary hydrocarbon, in normal conditions it is colorless and without any smell. It is slightly soluble in the water and it’s lighter than the air. Accumulating in closed space it is explosive at the content rate beginning from 6% to 17%. The most explosive concentration is 9,5%”

Methane is combustible but doesn’t combust by itself. This gas needs some oxygen to start burning. The question is: how much oxygen is it required for that? Special science which studies this question is called Stoichiometry; it is a part of chemistry about reagents correlation in chemical reactions. Stoichiometry allows to theoretically calculate required amounts and volumes of reagents.

To get the fire you’ll need fire situation, fuel and oxygen. Stoichiometry studies proportions of fuel and oxygen in burning gases. The fire doesn’t occur if there is too few or too much fuel. But correct proportion will provoke an explosion. It’s well-known that methane can be fired if its concentration in the air is 6-17%. Does it mean that if there is no enough volume of methane it will just burned away and with 9% volume it will explode?

Before to organize a great experiment the busters have made a small box (with 25 cm edge length) to have the possibility to easily control a percentage content of gas in the box. The first test was made at the lowest Stoichiometry rate – 6% of methane. As a result there was a small explosion which tore the box to pieces. Conclusion: 6% is explosive.

To check the legend in reality there was carried out a series of principal tests: in the assembled house there was created condition similar to ones in the movie about Borne.

Experiment 1: a magazine was put in a toaster with opened gas supply in a room. Some times later a magazine burnt up but methane didn’t inflame. Even 1 minute later there wasn’t even an allusion to Hollywood explosion. Methane together with fire didn’t cause the explosion. Destroyed this legend Adam and Jamie continued making experiments.

Experiment 2: what’s going to happen if you reach required gas and air proportion? A mixture of methane and fire not always cause an explosion – there should be an ideal correlation. The busters decided to fulfill a room with methane from the cylinder to get a correct concentration. Toaster was replaced by a log from the fireplace (burning time – 1 hour minimum). The log will burn till the moment when the volume of methane reaches 6%. Will the inflammation happen? Will it be powerful enough? After 4 minutes of log burning the situation turned to dramatic results: methane started distributing the fire all around the room, everything started inflaming. The busters shut off the gas supply and put out the fire in the rest of the burnt room. Hollywood explosion didn’t happen. The percentage of the methane rose to required amount but it just inflamed the room.

The busters didn’t stop their experiments. A stake was put to bigger volume of gas.

Experiment 3: Methane – 9%. There was made a new house which was more durable. Methane fulfilled the room through a hose, proportionally mixing with the air by ventilators which made air stream together with dangerous gas concentration circulating. Experts used a neon converter as a fire resource. Methane fulfilled the room. Three! Two! One! Fire! Spectacular representation succeeded. Explosion (it wasn’t an explosion itself, just fast inflammation) broke a wall. However a fire went out by itself.

So, the legend is destroyed. The myth is dismissed.

This is an ideal example of the fact that movie and life are different things.

 
 
 
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