MythBusters

Please don't try anything are you about to see at home.

We're what you call experts.

On this episode of "Mytbusters"--

Two, one, go--

Awesome.

Adam and Jamie get down and dirty...

I've never seen anything like that.

testing out an explosion inside a sewer--

The sewer's getting pretty full of methane.

turns manhole covers into missiles.

It's killing me.

Then, Kari, Tory and Grant take on the fun fabel

Love when I get to drive.

that trucks bedliner is indestructable

with car crashes

I'm okay.

angry attack dogs,

and ends with a bang finale,

can bedliner really save your life?

A lot of people ask me,

do you ever get tired of blowing stuff up.

I tell them no.

Who are the Mythbusters?

Adam Savage.

Am I missing an eyebrow?

And Jamie Hyneman.

Things are getting start a little crazy here.

Between them, more than 30 years of special-effects experience.

Together with Kari Byron,

I'm going to wreck this car.

Tory Belleci--

We survived.

and Grant Imahara--

Save yourself!

They don't just tell the myths.

They put them to the test.

So is every story we do an excuse for you to wear a

funny hat?

You should know the answer to that by now,

although specifically in this story it's quite apt

because we're doing a myth about sewers.

You mean like from a methane build-up?

Yes, but not just methane explosions

it's about during a methane explosion

do the manhole covers above the street,

above the sewer, get blown high into the air?

That sounds like a classic,

It's perfect for us.

I totally agree.

It's no myth that the decay of waste inside sewers

makes them the perfect breeding ground for combustion.

However, could a stray spark trigger an epic explosion

and send manhole covers skyrocketing?

Could a manhole ever turn missile?

What's the plan?

Well, it seems clear to me that

this has to end with us testing it full scale.

We need full-size manhole covers over a real sewer.

I agree. But you know what,

before we lock in on a full-size plan,

Let's do a small-squall one first

and see if we can learn anything.

Sounds like a good idea.

This ought to do it.

So to find out if a methane kaboom can make manholes fly,

the mythbusters get their minds into the sewer.

This is a schedule 80 steel pipe,

and I'm about to make it into a miniature sewer

with a viewing port all along one side

which is hopefully going to be explosion-proof.

This cumbersome pipe

should hopefully replicate a sewer in miniature,

but with great weight comes great responsibility.

You see us build a lot of stuff on this show.

And a lot of times it seems kind of like jazz.

We are really just figuring it out as we go along.

It's beautiful.

but when you're build something this heavy and substantial,

you can't quite do it that way.

You actually have to plan two or three steps ahead.

Let's weld this puppy down.

Because everything you're doing and

everything you're going to do is going to require

moving hundred of pounds of steel around.

Oh, this is heavy.

Not only will it make it logistically difficult,

but finger can be lost, eyes can be poked out.

It's dangerous.

Watch your fingers.

It's lovely.

Yeah, it is.

I can't believe this is a small scale.

It may be big,

Perfect.

but to a stand methane explosion it has to be.

And to complete the authentic aesthetic,

Jamie need to make these.

That's the manhole cover.

It's clearly in a sewer there's also waste,

human waste, household some waste.

And those wastes produce the dangerous gases

that can lead to an explosion.

That's not how we're creating our gases.

Now, we're calling up the store

and bringing in methane and pumping it in.

But remember, methane is tricky.

It requires a precise ratio of air to gas in order to explode.

9% in three --

that's exactly the ratio that we'll be using today.

Why?

Because this myth isn't really about

the circumstances that lead to an explosion.

It's about what happens afterwards.

The question we're answering is

will those manhole covers fly sky high?

To find that out,

Adam and Jamie are going to test

a series of potentially explosive sewer scenarios.

The first test is the most standard sewer setup--

an open-ended system.

Here's how this procedure is going to go down.

First, we fill our chamber with this -- methane.

Exactly .12 cubic feet, or stoichiometry of

9.5% gas to air by volume.

All right, you ready? I'm going to turn on the gas.

I'm ready.

Okay.

That gas will flow into the chamber until

it's the correct amount, then we shut off all the valves.

Then we mix the air and the gas with this--

this little whisper fan.

We turn on this fan for exactly two minutes,

let the air and the gas get together.

Nice looking rig.

Yeah.

that might be in the running for

the heaviest small-scale thing we've ever built.

At that point, we will plug in this neon transformer,

set the spark, and hopeful ever --

getting the manhole cover launch of our dreams.

But will the free flow of air and

gas in the open-ended sewer mean the manholes fly?

This is drain disaster,

open system

in three, two, one, go.

That was totally boring.

Like--

Wait. Let me do that again. Hold on--

Despite igniting methane at its explosive ratio,

the manhole covers didn't get air.

Manhole cover check one, two, three,

all still on.

I don't think an open system is that energetic.

No.

And the reason for that lethargic blast?

Well, for that, it's over to the Hyneman.

Think of this like a gun.

If the back of the barrel is closed,

then the exploding gunpowder goes this way and

pushes the bullet out the end of the barrel.

However, if that breach is open,

the the gas is going to follow path of

least resistance and escape here.

And it's not going to do anything to the bullet.

It's not looking good for the open system.

But this myth doesn't rest there.

I'm making a mess for science.

There's a whole lot more manhole mayhem to come.

Next up is a fan favorite with three times the carnage.

All right, you guys are familiar with bedliners, right?

Yeah, the stuff you spray on your pickup truck bed

to protect it.

Right. Now officially it's minimumly to stop scratches,

dents, and rust.

But unofficially, people are claiming

that it is practically indestructable.

Yeah, there's all kinds of crazy stuff on the fans sites,

that you can make it dog-proof,

you can make it car crash-proof,

you can make it house blast-proof.

And soon we're taking most damages and testing, right?

Exactly.

Bedlineders, used to line the beds of trucks and

protect against dings and scratches.

According to fans, that's not all.

Supposedly it can defend against damage in

a host of unconventional conditions.

So we're gonna be working with attacking dogs,

crashing cars and exploding houses?

I think I love this myth already.

Before we get too far,

let's find out what the bedliners made up

and how it performs under normal condition.

Buzz kill.

Science.

You want to find out about bedliner?

I've got a few questions.

First it's time to bed down

and find out just how this stuff works.

Mark, what exactly is bedliners?