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Pyrotechnics: Blowing Up a Car

8 September 2009 30,564 views 8 Comments
This post is one of a series of entries that will be talking about some of the things I did while at the NFTS (2006-7).

Back to School

There’s no doubt that leaving my job at Lionhead Studios to go to film school for a year was a risky move for me to take. It was a tactical decision to try and rebrand my career towards film and commercials work; something that I’d been trying to do for a while.

CarBang_FireFront

One of the other reasons that I decided to sign up for the VFX/SFX course run by the NFTS was because of the pyrotechnics module that they offered. Having grown up watching films like Raiders of the Lost Ark and being utterly consumed with fascination about the stunts and effects, I felt that this was my opportunity to satisfy that craving.

I wasn’t disappointed. Not even close.

The Setup

There were six of us on the course: Kate, Kia, Mattias, Nick, Seru, and myself. We were all from a wide range of backgrounds which made for an great mix of skills and experience. The first month on the course was spent learning about fire, explosives, rain, snow, firearms, and many other areas that an SFX technician has to have a good understanding of. The car explosion stunt was the climax to the course module.

I’m not sure where the idea came from, but I think I suggested that it would be a cool idea to blow up the car with a rocket launcher. I figured that blowing up a car without a good explanation would be a bit dull. Far better to make it look like we were hitting it with an RPG. Michael Bay eat your heart out!

One thing we all learnt in that first month as trainee SFX technicians: in a low budget scenario, you literally need to beg, steal, or borrow whatever you need to get the job done. Resourcefulness can make the difference between getting the shot, or not.

The begged items came from Graham Brown in the form of fishing wire and some fireworks. Although to be honest, I didn’t need to do too much begging. Graham as usual was more than happy to help out.

CarBang_RocketLauncher

In true Blue Peter style, the rocket launcher was made from a cardboard tube; this time, stolen from our communal TV room at the film school (it was in a pile of rubbish and no one was using it). I painted it green, and fixed a wall bracket to it as a makeshift sight. A bit of yellow and black tape finished it off.

CarBang_SteeringWheel

To make handbrake turns easier, I rigged the steering wheel with a cylindrical door handle borrowed from a door found on the NFTS main stage. I should point out that it wasn’t from a real door, just one that was lying around previously used as part of a set on an earlier production. Before we blew the car up, I got it back and reattached it to the door the next day.

CarBang_ArriCameras

One thing I didn’t mention in the guerrilla SFX “beg, steal, or borrow” toolkit was bribing. The NFTS course managers persuaded Arri to come along with some of their high speed cameras. Not through any monetary bribing (this was low budget, don’t forget), but as a promise of some great stock footage for any of their product demos. In the end, they brought two cameras which, despite the poor light conditions, were run at 200 fps and 400 fps.

The Car

We didn’t have any sort of story line or plot as we were more interested in the SFX, but we still wanted to shoot some footage with the car. If we’d had two cars it would have been better, but again, our budget didn’t stretch that far. So we kept it simple and just used the deserted market stalls as a background for some interesting shots.

You might be surprised how tricky it is to do a handbrake turn in a Ford Escort, even in the wet. It took a bit of practice but I got there in the end. The door handle on the steering wheel helped, but I found the key was to initiate the turn, slam on the brakes to throw the weight forward, and then yank on the handbrake to throw the rear end round. The one that you see in the video nearly went 180º.

CarBang_EmptyRear

After we’d done the other shots with the car, we did a final run ending up with the handbrake turn. With the car in the final position, we set about stripping it down to remove any dangerous or unnecessary parts. High on this list was the petrol tank which was drained and removed. We were also told that the pistons for the hatchback boot can be highly dangerous in a fire and can explode violently. Apparently the fire services are quite nervous about these things going off in motorway fires!

Other things that were done: the car battery was removed, tyres were let down, brake fluids and oil were drained, and many other parts were removed. All this was to make sure that we didn’t have any unpredictable results that could be a safety hazard, and also because we didn’t want the car to burn for hours after the explosion.

In case you’re wondering, the car had been bought for about £300 specifically for us to blow it up. Coincidentally, it bore more than a striking resemblance to my own car at the time so I swapped the wheel hubcaps as they were better than mine!

Rigging the Explosives

CarBang_BonnetAfter the car had been stripped down, we set up the charges. Unfortunately, there’s a limited amount of detail that I can go into without being a bit irresponsible by telling everyone how to blow stuff up, but suffice to say, we used several standard petrol based mortars along with a couple of charges to blow the windscreen.

CarBang_Boot All the charges had to be wired up with long lengths of electrical wire so that we could be at least 50m away when it went off. The charges were connected to a custom made detonation box belonging to Graham.

CarBang_FishingWire

The rocket launcher (err… cardboard tube) was connected to the front of the car by the fishing wire. We sellotaped a firework rocket to a drinking straw that had the fishing wire threaded through it.

During the set up, we were all aware that it was a race against time. Being November we had a limited amount of daylight, and it was made worse by thick cloud cover and drizzling rain. Trying to film something as bright as a fiery explosion isn’t something you want to do in complete darkness, especially with high speed cameras. You’d see either the explosion or the surroundings, not both; at least not in any detail.

Bang!!

So when the time came to set everything off, we were knackered. Making sure that all the cameras were up to speed, we gave a countdown and lit the firework. It shot along the fishing line, hit the car, which blew up in a series of explosions, one of which sent the windscreen 30 feet into the air. Everything worked perfectly and at the right time; something that we were all surprised by considering the pressure we had been under and the weather conditions.

CarBang_Explosion01CarBang_Explosion02CarBang_Explosion03

CarBang_Explosion04CarBang_Explosion05CarBang_Explosion06

We had spent a lot of time carefully laying out and labelling the numerous cables that were used to set off the explosions. Since we had limited resources, many of the cables were made up of two smaller ones, so we had to make sure that all connections were working. I think we checked everything at least twice. Graham’s firing box had a special mode for testing connections by sending a low powered current down the cable and through the charge. It wouldn’t be enough to detonate the explosive, but enough to be able to check the continuity of the circuit. We would still treat it as a live firing though… just in case.

Safety First

There are lots of precautions one takes when working with explosives. While I said that I wouldn’t go into any details on how to make something go bang, I think it’s safe enough to discuss some of the safety measures we took.

CarBang_FireFront

You have to be very aware of what everyone is doing, especially when you are connecting the charges to the lines. For example, it’s all too easy to leave the battery connected to the firing box with the key in the on position. While that wouldn’t detonate the charge (you’d still need to press the right button), it’s not a situation you want to be in. The standard Health and Safety strategy is that it’s everyone’s responsibility to look out for each other, and to make sure that these slip ups don’t happen. It’s all about minimising risk.

CarBang_FireBack

Generally you don’t want to be wearing anything that has a tendency to create static electricity. It is possible (although unlikely) that static can generate enough power to set off a charge. Synthetic materials are well known for being good sources, so they should be avoided.

This one’s important (and you’ll recognise this if you’ve ever bought fireworks). Never return to a charge if it doesn’t go off. There’s a procedure to follow in this situation. Generally the safest thing to do with a dud is to place another charge next to it, and detonate one using the other. We were shown a video of what can happen if you try to take shortcuts. I believe the poor chap lost hearing in one ear and part of a finger.

CarBang_FireCam

The best way to make sure a charge is safe is to twist the two connections together. It makes sure that there’s no potential difference between the wires so it’s impossible for the charge to be set off by a voltage. Most pyro charges are supplied in this configuration. Of course, there’s no guarantee that you won’t set them off with excessive or prolonged exposure to heat or some type of chemical agent, so you still need to take care.

Other Considerations

CarBang_FireServicesWhenever you do any sort of pyrotechnics work, it’s nearly always a good idea to let the local emergency services know in advance. With an explosion as large as the one we did, it would be pretty likely that someone would call the fire brigade – which they did. About ten minutes after we ignited our Ford Escort bonfire the fire services turned up, blue lights flashing.

CarBang_FireExtinguish

If we hadn’t spoken to them first, they would have charged us a call out fee. They were a great bunch of guys though, and were probably happy for the break in their routine. The NFTS also did a leaflet drop in the area a few days before so that local residents wouldn’t be alarmed.

Graham Brown was our pyrotechnics tutor and supervisor. He worked for many years at the BBC providing special effects work for a huge number of different shows. When he’s not tutoring at the school, he still does work on a freelance basis for shows like Waking The Dead (which I was lucky enough to assist him with on three occasions – more in a future post). I’d like to take this opportunity to thank him for all his enthusiasm, dedication, and hard work, and for such an amazing experience that I’ll never forget.

Thanks should also go to John Rowe and Sarah Hayward, the course directors, who worked tirelessly to make sure our time at the school was chock filled with fun things like this to do. And finally a big shout out to the other guys on the course – those were good times eh!

CarBang_TheTeam
Rear, left to right:
John Seru, Kate Walshe, Mattias Engstrom,
Nick Preston, Kia Coates, Andy Nicholas.

Front:
Graham Brown

(And then we had to clear up the mess)


The Video

Here’s the final cut with a wee bit of compositing to make it look like the car was still moving when we blew it up.

Video not available
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8 Comments »

  • john seru said:

    BOOOM!!!, that was quite a day, next time we should add a jump!, nice blog post…

  • AndyN (author) said:

    Yep, the good ol’ days eh!

  • Chuong said:

    lol,
    It must have been very fun to blow something out like that :D. BOOM fantastic

  • Diego Guglielmi said:

    to make the car looks like it was still moving, you made a shot in wich it stops in a near position and the flash of the explosion hides the difference until image swap or u used a different method?

  • AndyN (author) said:

    Hi Diego,
    Yes, pretty much as you said. The shot where the car blows up was filmed exactly as you saw, but obviously the car was stationary. I just tracked in a stabilised version of a shot of the handbrake turn. The car ends up in correct position because we didn’t move it until we blew it up, which made the whole thing a lot easier.

    As you might expect, there was lots of roto work involved and I had to recreate the lens flares over the top as they were too difficult to pull from the other plate.

    And yes, the explosion hides a lot 😉

  • Diego Guglielmi said:

    rotoscoping to separate the explosion from the stationary car and stick it over the moving one?

    this is really intresting, im getting on with maya now (its quite buggy some times) but its widely used in here (uruguay).

    what do u know about shader programming? i tried once to get over renderman once (and planning to do it again)

  • AndyN (author) said:

    >what do u know about shader programming?

    I can turn my hand to it, but I’ve not had the need to for a while.

    Like most of these things, as long as you’ve got good programming skills and know how to mine the net for knowledge and learn from other people’s experience you can jump into most stuff. Assuming you know the concepts behind it.

    Best way to get into it is to read some basic books on ray tracing. That’ll give you a good overview of the techniques involved. This book is also required reading:

    http://www.amazon.com/Texturing-Modeling-Second-Procedural-Approach/dp/0122287304

  • Diego Guglielmi said:

    ive got that one in a pdf, however i should get over integral and differential calculus to understand it well (slow highschool)
    any way will do it by myself

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