Shooting Explosions

Fancy a giggle?

I need to put Stalex cameras on the ground floor of a 20 story building that will be demolished by explosives for a TV doc. We'll construct housings to protect the camera bodies. The cameras are rated to 100gs of shock in any axis, so its a simple matter of protecting them from 150,000 tons of concrete, cockroaches and asbestos. (contents of an average council block).

We will also put a camera on the roof, protruding about 8 feet and pointing vertically down. (I did this shot a few years ago on video, can't wait for a 500 FPS version)
Another camera will be on a ledge toward the top or perhaps being winched up the side of the building as it crashes to the ground...As ever, it's the little details that need to be addressed and solved to improve the chances of success for these shots.

I hope you can help.

To improve image quality we can choose not to use a protective port on the camera housing on the ground floor and write off the lens. The interior ground floor shot needs to be quite wide, 100 degrees, so a 1 inch thick laminated filter will degrade the corners of the frame as well as require a much larger camera housing.
The budget does not allow us to write off 3 other lenses, unless protecting them will cost more than the cost of a used prime.
Other than a ceramic material, which has a dimpled surface and is a little pink, similar to a Tiffen Warm SFX 2, are there other flats that can be recommended?
Stacking filters has been suggested.

Any ideas for keeping dust off the lenses?
Am I right in thinking that fine dust particles will be repelled if we positively charge the front element or port? Much larger particles of grit that will be deposited as a result of being propelled into the element could be removed with a powerful blast of gas. Is there a device that can do this?

Lighting for the ground floor interior has presented a big challenge.
The ground floor external walls are knocked out leaving a floor, a ceiling and pillars. Daylight floods in - until the exterior walls are covered over with corrugated iron to contain blast debris. The interior space therefore is not conducive to a 500+ frame rate!

The lighting ideas so far are:

A) Flash bulbs from Megaflash in Ireland. They have a bulb with a 2 second duration. These can be rippled to produce a longer duration.
Usually used for small areas, cars, close ups of projectiles et. This could be an expensive option.

B) Remove ten sheets of corrugated iron from ground floor and replace with 6 mm polycarbonate. Light from 150 foot with a small thermonuclear explosion.( or 3 x 20k Arrisuns).However as the dust cloud develops in the first1/2 second after detonation, it will reduce the light level inside the ground floor. Also polycarbonate is £90 per 6x4 sheet .

C) Build disposable housings with a simple reflector for 10k bulbs.
Place inside building, probably about 12 feet from pillars. Any ideas on how long the bulbs will last? What would be a good choice of bulb?
Placing the bulb in a sealed polycarbonate tube may work.The advice from GE is to insulate the bulb from the floor to reduce vibration.

D) Same as C but place lights in holes in corrugated iron. They would be much farther away from pillars so we would need many more. I Can't be more precise until next week when we have anothe recce. But they would be a further 20 feet away from the blast so may last a few seconds longer.

E) Combination of the above.

The unknown factor in this shot is of course dust. Will it obscure the collapsing pillars?

UK Broadcasters are particularly touchy these days about filmmakers interfering with documentary subjects. So we have to shoot this for real. We cannot even cut-in a big close up of an exploding pillar, shot in another place. Pyrotechnics, for some added glitz, are out of the question too.

We will be satisfied just to get the beginning of the explosions
After we have seen the site we will conduct tests at an explosive research establishment in a few weeks. The shoot is probably in March, so plenty of sleepless nights ahead.
Any comments or ideas, no matter how off the wall will be appreciated.

Mike Brennan

>Any ideas for keeping dust off the lenses?

You could blow compressed air towards the lens flats.

As far as lighting, how about an array of china lanterns sporting 1000 watt bulbs? Obviously you won't have to worry about the lanterns catching on fire, and they're reasonably small so they won't obscure the view of the crumbling pillars. They are also quite bright and very cheap. Depending on how fast your lenses and film are and how large the interior is, the lanterns may provide enough light. Perhaps a combination of lanterns and
external sources?

ekiM.

How about the Hydroflex mattebox with a small tank of air (like those emergency scuba outfits?). I've used this with a low angle, very dusty dirt road situation to good effect.

Alan Caudillo

We have two shots to deal with, one is a camera on the 20th floor, positioned on a pole about 8 from the parapet looking vertically down. When I did this a few years ago the port became a little dusty 1/3 of the way down, with fine particles sticking to the filter, 2/3 of the way down the camera hit the rising cloud of dust caused by the lower 20 floors impacting the ground. This dust cloud was very dense and as the camera was moving at about 30 mph it was instantly smeared by larger particles of grit that would be probablyimpossible to remove with compressed air. An onboard system to clean the port for the first 3 seconds would be useful. A can of dust off sounds ideal but I am worried that if the can became inverted the propellant would be expelled and therefore, ice over the port!

Has anybody come across a pressurized dust off product that does not contain a propellant?

The cameras on the ground floor can have a pressurized supply of air no problem. Has anyone tried this under very dusty conditions? The duration of the shot is hopefully 3 seconds at 500 fps (1/2500th sec) on one camera and 1000 fps (1/5000 sec) on another for a close up, lighting budget permitting.

Mike Brennan

>Has anybody come across a pressurized dust off product that does not contain a >propellant?

Falcon made a nozzle that was attached to a hose, that was in turn attached to the can. That may be what you need. The can can remain vertical and the nozzle moved around and positioned where you want.
Auto racing ran into ( pun intended) a similar problem, and came up with a moving shield. Perhaps some sort of Disk, that spins and has the Shmutz ( a very technical term) removed?
By the way what is a Stalex Camera?
About not protecting the lens, it might be a possibility to dammage the camera where the lens mounts to it?

D) Same as C but place lights in holes in corrugated iron. They would be much farther away from pillars so we would need many more.

This sounds very exciting visually wise, especially when the dust first begins to rise.

I guess in this case the old standby advice "TEST TEST TEST" doesn't apply.

Steven Gladstone

EkiM wrote :

> As far as lighting, how about an array of china lanterns sporting 1000 watt bulbs?

Thanks, that a good idea and cheaper than 10k bubbles and holders, (£180 for a 10k bulb and £40 for holder) The concept of 60 to 100k of tungsten in the same area as detonating cord and explosives has still be addressed by the demolition team!
(haven't told them yet....)
Eposures are 1/2500th sec for the 500fps wide shot and 2500th sec for the close up.
We may have no option other than to use HHIs. A Arri X light head is about £3000. If we could protect them they would be my favored lamp. Has anybody used HMIs under strong blast conditions?

Thanks

Mike Brennan

Sounds like fun...do you get to yell "Fire In The Hole!!!"

For the dust...creating a very high pressure zone in front of the flats would be my choice. In my non-linear editor I have 5 12v cooling fans that move 100 cuft/min each. If four of these were mounted in ports on a hard matte box that was sealed to the flat, each with its' intake side covered with fiberglass wool so you are not re-circulating dust, powered by a car battery.....it might do the trick.

For light...flo's/nook lights/bare bulbs mounted on the backside of the pillars and above the cut line of the explosives....they will put some light the next pillar in line, provide some shape to each explosion and by lighting the developing dust clouds behind each pillar, will create a lighter valued background, making it easier for the pillars to stand out.....for awhile at least. With whatever approach you choose, lighting the clouds of dust should be part of what you do.

How about putting some cheap laser pointers in there.....attached to the pillars you can create a grid in the smoke that may give a nice visual of the collapse when the smoke has obscured everything else.

Glenn Suprenard Dir/DP

>Auto racing ran into ( pun intended) a similar problem, and came up with a moving >shield.

Panavision has one of these devices. I saw it used to prevent water from splashing on the lens. It's a plexiglas disk that spins, throwing the splashes outward. I'm not sure how well it prevents against dust though.

ekiM.

.25" clear polycarbonate plastic would be good for protection "if" it is well secured so that it doesn't implode into the lens. The unsupported area of the filter should be as small as possible to reduce the amount of pressure it has to withstand. The amount of distortion might be acceptable even with a wide lens. One problem is that it does attract and hold dust more than glass.

There is laminated glass that is thinner than 1". But you should ask the manufacture if it will withstand the pressure.

Can you mount used Nikon lenses? That would keep the cost down of a total loss. One trick the atom bomb photographers used was a 45 degree mirror to reflect the shot into the protected lens. Good only for longer lenses of course and only until the first pressure wave.

>Any ideas for keeping dust off the lenses?

Air nozzles is a good solution. Props dept. has done this for us. We had to use two wide fan shaped nozzles with a lot of pressure to keep the dust off. This one you can test out before hand.

>Lighting for the ground floor interior has presented a big challenge.

Others have suggested quartz halogen T3 bulbs which come in at least 1500 watts. This sounds like the least expensive way of doing it (the cost about $15 each here in the US). A sheet metal shop should be able to make some inexpensive reflectors.

Good luck & have fun!

Don Hayashi

>Auto racing ran into ( pun intended) a similar problem, and came up with a moving >shield. Panavision has one of these devices. I saw it used to prevent water from >splashing on the lens.

I've seen one of these devices also, on the cover of Kevin Brownlow's biography of David Lean (A great read, BTW)

On the subject.... Did I read correctly in a prior post that you are considering the use of HMI lights with a prism/drum camera at ultra High speeds? Am I wrong in thinking that this isn't possible, since your fps rate will far outstrip any kiind of AC arc light, flicker free or otherwise?

Have you discussed any options with your pyrotechnical folks about the possible use of something like magnesium flares as a lighting source? If they lay them down as part of the "charge", are you still subject to the admonishments of documentary purists. I'm not sure if I'm ready for that vow of chastity, myself.

Hope your shoot is a real blast!

Joe Di Gennaro

>Am I wrong in thinking that this isn't possible, since your fps rate will far outstrip any >kiind of AC arc light, flicker free or otherwise?

I have shot at 1/5000 sec shutter speed with my Arrisun 1.2 flicker free.
There is occasionally some flicker on the edges of the beam though, but nothing to worry about.
Magnesium is a brilliant idea but for its flickering nature and the large smoke cloud it produces. I recently tried to buy, from a defense supplier, the type of flare with a parachute that are dropped over battlefields. We needed it for a dramatization of a UFO landing.
Very difficult to get hold of!

Thanks
Mike Brennan

>Has anybody come across a pressurized dust off product that does not contain a >propellant?

How about designing a rig that blows pressurized air across the lens with the air piped-in from a compressor off-site or next to the camera?

Also, I recall seeing promo literature awhile back for HMI pars (4K-6K?) that were designed with both underwater housings and explosion housings.
Wasn't it LTM? I remember thinking, 'gee how many calls do they get for the explosive proof housings?' Anybody familiar with these units?

Jim Sofranko

Mike, Et al.

I'm gratified to hear of your success with flicker-free HMI lights and prism/drum High speed. I'll be tempted to try it on my next Photosonics gig.

I thought further about your needs for a somewhat expendable, powerful light source:
Understanding that you might be in a very explosive environment (literally)
Have you given any thought to using the guts of an old carbon arc light? I realize they normally would require an operator to strike them and keep the anode trimmed, but depending on the lead time between the final walk through the building, and the detonation, perhaps they could be "struck on the run" and left to burn until the boom!

Joe Di Gennaro

Now...here's the cool way to do it.

From what I've seen watching doc's on demolitions...they blow the pillars in
a sequence to get the building falling in a pre-determined direction.

What would it take to mount the camera on speedrails and get up enough speed
to start rolling on the first pillar and back out of the building just ahead of each explosion, staying just infront of the dust cloud.

Anyone belong to an amateur rocket club?

Glenn Suprenard Dir/DP

>How about designing a rig that blows pressurized air across the lens with the air >piped-in from a compressor off-site or next to the camera?

Hello all :

I just did a shot yesterday of a carpet cleaning "wand" pulling past/under an extremely low mounted camera. This wand is around 150 degrees F and has 6 steam jets. I was very concerned about potential lens fog. I had the prop guy bring in an aircompressor which is filtered for airbrush painting. These produce an oil-less/clean pressurized air which can be regulated. We rigged it to blow across an optical flat and it worked great!

Jeff Barklage

>What would it take to mount the camera on speedrails and get up enough speed

to start rolling on the first pillar and back out of the building just ahead of each explosion, staying just infront of the dust cloud.

Anyone belong to an amateur rocket club?

Come on Glenn, you know you want to be in there on a dolly with a grip pushing you, the Ultimate one take shot.

Steven Gladstone

>Come on Glenn, you know you want to be in there on a dolly with a grip pushing you, >the Ultimate one take shot.

Didn't think I was being that obvious.

Hey...ya' know those cable rigs they use to yank stunt people off horses or launch them during explosions. Heck, with a pulley system, a couple hundred feet of cable, a hundred foot crane and a few hundred pounds of counter weight ..why...you could shoot this hand held.

Glenn "Ready when you are C.B." Suprenard Dir/DP

Mike you said for a giggle !!

Well from Justin's "Stupid ideas R us" file comes this one :)

Get Kodak to let you have a length of safety base as long as your drop and 70-80mm wide. Work out a channel for this past the lens and a feed canister on one side. Either pull it past the lens with a motor or (better I think) attach the free end to an open umbrella. This would have the advantage that it would go quicker the further it has fallen also you could extend a bit of string to the top of the building so that the umbrella would not get stuck with the falling masonary ...

No I'm not drunk I'm like this all the time.

Justin

I had thought of a more British way to create the same effect- a bungy rope!

It could be pre tensioned across the ground floor and then its tether simply severed by the first explosion. It would fly across the ground floor, say 30ft in perfect unison with the sequence of exploding pillars. The problems with moving the camera quickly are possible blurring of the picture and snagging on of the many detonation cords that stretch across the ground floor like a spiders web! Then there is the problem of extra areas to light. The light from the explosion is of course at an acceptable level but its duration is for about a1/10th second. A perfectly timed tracking shot full of one pillar exploding after another would work- on maybe the 5th take!

A track on the outside of the building presents no hazards to the demolition team. Moving the camera would make the shot much more interesting and if timed correctly would make for a take of much longer duration. When we recce I'll
keep an open mind about tracking...

We are also considering a simple pulley arrangement with the camera at one end and a counterweight at the other, at the top of the building. The first explosion severs a tether at the camera end, releasing it to be pulled up the side of the building. Chaos would ensue when rising camera meets falling roof.

To keep the camera shooting straight we need two cables and a elaborate pulley arrangement at the top. The director loves this idea I hope we have the budget to try it, although I'm not sure that the dynamics of the building falling down will be lost by the camera moving up.
Thanks for all your input I appreciate it

Mike Brennan

>I thought further about your needs for a somewhat expendable, powerful light >source : thought to using the guts of an old carbon arc light?

They are a excellent choice but for the trimming.
Unfortunately their is a period of one hour or more after the final walk around before the demolition takes place. The final walk around is conducted by one man. (when I put a camera on the roof of a 20 story building this was the guy that had to go through a complicated procedure to power up and roll a video recorder and re secure the housing. What a guy!)

Is there a way of remotely trimming carbon arcs?
Cost of DC cable could be a factor too.

Mike Brennan

>A perfectly timed tracking shot full of one pillar exploding after another would work- >on maybe the 5th take!

Get the camera rig moving before the first explosion to get up to speed and even if the explosions catch up to the camera, that would be a nice shot.

I have made a tube dolly with opposing concave wheels, the dolly platform was a high hat on a pancake. The tube was PVC and the dolly was mounted from the end of the track and locked onto the tube. If you attached your bungee to this, left the end of the track open with out a stop and at building opening, it might build up enough speed to launch itself clear of the building. Think of it as a slingshot.

Also, if the dust from the explosion is going to limit what you can get, why not shoot on the floor above. The building collapse could be thought of as a more important theme than the explosions that started it.

Glenn Suprenard Dir/DP

>Is there a way of remotely trimming carbon arcs?

Actually, there is. The anode and cathode rods are fed into the lamp housing by a pair of corkscrew like devices, which act like slow turning electric pencil sharpeners.

The problem is that the longest rods I know of will only burn for about twenty minutes. I don't know of any way to remotely strike the arc. I'm not sure if your demolition engineer will be knowlegable/comfortable striking up. Perhaps someone like Mark Weingartner can offer some advice, having been a sparky kinda guy for many years.

Sincerely,

Joe Di Gennaro

Regarding lighting the demolition of the pillars in the boarded up ground floor. You might consider magnesium flares. They last for several minutes, they create a tremendous amount of light, and are disposable, so there is no great expense of trashing a lighting fixture. Of course you would have to do some tests to see just how much light they make. And also to see if the explosion shockwave will "blow out" the flare, but I doubt it would. Once magnesium is ignited, there is not much that will put it out. You will have to develop a remote method of lighting the flares.

I've never done this, but it seems like a great way to make a tremendous amount of light, in a reliable manner, for relatively little money.

Bill Bennett

Didn't LTM or someone have a series of HMI pars that were both waterproof and explosion proof? I recall seeing literature of that nature several years ago. Anybody have experience with them?

Jim Sofranko

Hi Jim,

In my early experience with LTM units, I think it may have been "explosion PRONE" that was the norm.

Jerry (speaking for myself, as usual) Wolfe

I can't help feeling that we are all referring to HMIs that are sufficiently sealed as to be 'intrinsically safe' ie they won't cause an explosion in an explosive atmosphere. I'm not sure _any_ lamp would survive a direct hit...

One small point. I seem to remember from filming in a quarry that all the force should be held within the object being blown up. So a well controlled explosion is rather unspectacular a all you see is the rock face slowly separating from the rest of the quarry.

Still, I'm glad that OpTex doesn't have high-speed cameras, I think I'll give this one a miss!

Brian Rose

>In my early experience with LTM units, I think it may have been "explosion PRONE" >that was the norm.

YeeeOoouch! Yeah I recall working with the smoke and sparks of the early HMI's as well as those huge, heavy ballasts. Amazing how much more durable and lighter HMI's have become in recent years.

Jim Sofranko

>And also to see if the explosion shockwave will "blow out" the flare, but I doubt it >would.

Magnesium creates its own oxegen when ingnited. It burns fully submerged in water.
As for flicker- i've not noticed this. it burns very white, towards the blue end if i recall rightly.

caleb, New Orleans based, has shot by 'Flambe' during Mardi Gras

Bill wrote :

>You might consider magnesium flares. They last for several minutes, they create a >tremendous amount of light, and are disposable, so there is no great expense of >trashing a lighting fixture.

Has anyone used, or shot with magnesium flares? What colour temp are they?

In the good old wild west they are probably available at 7 Eleven, but in the UK, more difficult to buy.
Any suggestions for suppliers?
If we can get hold of them we'll try them on our test day.
Mike try anything once Brennan

>I can't help feeling that we are all referring to HMIs that are sufficiently sealed as to >be 'intrinsically safe' ie they won't cause an explosion in an explosive atmosphere.

I think someone needs to explain the misnomer "explosion-proof".

The term "explosion-proof" as used with lighting units means that the units are sealed in such a way as to not CAUSE explosions in a dusty or volatile atmosphere. It DOES NOT mean that they will SURVIVE explosions, although they may have a better chance of survival than non-explosion proof lights, because of their housings.

As for the current issue of filming a building demolition, I would first talk to the demolition team themselves. Most of these outfits regularly film or tape their work, partly for the publicity and partly to study the blast process itself. They may have plans to record the event themselves, or at least have experience with recording past building removals.

Doug Hart

Another possible source of magnesium flares is to contact a fireworks manufacturing or aerial display group. If they can not provide the flares and the expertise of how to remotely light them, I'll bet they would know who to call.

I found several fireworks manufacturers and aerial display companies with an internet search. Seems worth a try.

And by the way, I'm pretty sure I am not the only one here that wants to hear how this one turns out! Besides the difficulty of lighting the shot, I want to know how you are going to protect the camera from the thousands of tons of building that are going to fall on it.

Bill Bennett

One of the leading manufacturers of distress flares is Pains Wessex in UK at the following site www.painswessex.com/

After speaking with them I'm too sure that they are an option for my demolition shoot. They produce a lot of smoke and they burn at 2000 Centigrade.
They are set off by first twisting a cap and then striking it firmly, so setting them off by remote control is a problem. The brightest burns for 40 seconds. We would have to confine the smoke in the building and away from our shot. The demolition company do not want a smoking building just prior to demolition. Doesn't look good on their showreel! They have put me in touch with a ex employee who makes fireworks and who is willing to make a one off that could be electrically ignited.

How will we protect the camera? Basically, there will be a precision built steel case around each camera made of 1/2 inch steel. This will be lined with 1 inch of very high density foam, (not much foam I know but the Stalex cameras can take 100gs whilst shooting) This will form the "new" body of the camera.

We will then protect these bodies against varying hazards.

For instance, the cameras on the ground floor will have to withstand the impact of the weight of the falling concrete, followed by the build up of pressure caused by the weight of the 20 floors above "settling" onto the debris pile. We can calculate the pressure with some basic arithmetic. If the building weight is about 150,000 tons and the debris pile has a footprint of about 100 square feet then on average the weight on any one square foot is 15 tons. To accommodate this the cameras on the ground floor will either have another steel box around them, or an arrangement of concrete slabs forming a cubby hole or both! We will also weaken the floor to create a survival space underneath the camera. The outer case will be about about 30 x 30 x 30 inches and constructed of 1 inch thick flame cut steel plate. This box will take a direct hit from the pointed end a 500 kilo concrete slab, traveling at 40 mph.

At least that's what my engineer says....

The cameras that are on the roof, traveling down with the building need to be cushioned from their impact, of 32 mph, with the debris pile. They will be housed in one of the 1/2 inch thick steel boxes lined with foam. On the outside of this box we will secure a energy absorbing material that is lightweight and cheap. Materials that we have been investigating are aluminum honeycomb, as used in the auto industry (expensive), air tight plastic bottles, as used by paragliders (effective but bulky), rubber tyres (springy- the camera may end up 2 blocks away!), high density foam, formed into wire mesh box (effective but expensive). The last/first time I did this shot the video equipment was little damaged and we constructed the box without any impact absorbing material on the outside. The box ended up on the top of the debris pile, so we just walked up and hauled it away!

I hope we have as much luck on this shoot

This weeks "in" list
Flash bulbs from megaflash in Ireland www.meggaflash.com
1000w bulbs from DIY shops for £1.20 each
Compressed air
Unbreakable Polycarbonate
Honeycomb aluminum
Cost/performance ratio of plate steel

This weeks "out" list
Exec Producer, who won't let me near the demolition team just yet (thinks I'll frighten them off-Ha)
Unworkable polycarbonate
1000w bulbs from DIY shops that have nickel contacts that are impossible to solder
Cost of puppeteer on shoot day to manipulate cables and strings to set off compressed air, flash bulbs, roll cameras winch cameras, close hatches ect ect
Cost/performance ratio of physiotherapy.
Cost of sniffer dogs ...

Mike Brennan