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The Art of Pyrotechnics

Pyrotechnics is a very generic term for most things that have an energetic composition that is combustible or explosive.

This section will help you to understand how pyrotechnics are used in the entertainment industry, how they are made and what they do! There is a section here about everyone's favourite subject - High Explosives!

What are Pyrotechnics?

Pyrotechnics - or pyro's as we call them are devices that are similar to fireworks but are precision made and usually designed to be used in close proximity to persons. They are usually fired by electricity and are instantaneously ignited

Below is a load of information about pyrotechnics, including Igniters, Effect Types, Firing Systems, Wiring and High Explosives.

 

Igniters

Igniters are the key to pyrotechnics, they turn the electricity into the fire that starts the composition burning, this is why sometimes they are known as electric matches. Some people incorrectly call igniters "Dets" or "Detonators", this is not the case as a detonator is a completely different device that is only used to initiate high explosives. The term electric match can be very misleading, a match flares up and burns for about a second, however most igniters explode in a fraction of a second.

Igniters are very similar to a light bulb or a fuse. The current is supplied via 2 wires, across the 2 contacts is a bridge wire that is made of nichrome wire. When a current is passed through this wire it burns out creating a very small white spark.

A sensitive pyrotechnic composition is then pressed over the bridge wire. The composition is usually lead styphnate, but because the composition contains lead, new lead free alternatives are now becoming available.

The lead styphnate it then dipped in a protective lacquer which when dried protects the head form the elements, damage and also insulates it from static discharge.

Most firework accidents involve an igniter, this is because the lead styphnate is extremely sensitive to impact, static and heat and friction. It is widely known that igniters will fire if cut with a pair of scissors, a majority of firework fusing accidents happen this way. Igniter manufacturers have devised simple ways to protect users form this form of accident and they are available with plastic shrouds or silicon tubing protectors. In France it is illegal to remove the plastic safety shroud from an igniter. Unfortunately in the UK many companies opt or the cheaper un protected igniters.

Below are some specifications of the 2 most popular igniters:

 

Davey Bickford N28F

Martinez E-Max

Resistance

1.6 ± 0.3.0Ω

0.9 ± 0.15Ω

Maximum Current for Non Functioning

0.3A

0.3A

Minimum Current Required for Functioning

0.55A

0.55A

Advised current for functioning

≥ 1.35A

≥1A

Average Ignition Time with Current (I)

1.8ms at I =2A / 0.85ms at I =5A

Unknown - but faster than DB

List of Igniter Manufacturers:

  • Davey Bickford
  • Martinez Specialties
  • Oxral
  • Luna Tech
  • ICI

Below is a picture of igniters from Davey Bickford and Martinez, also below are some interesting pictures of igniters at various stages of ignition.

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Pyrotechnic Device Types
Gerb

A Gerb is a fountain effect. When fired the device produces a column of silver or gold sparks. Gerbs can be very varied, they can be small (1 meter high) or large (20 meters high) and can vary in duration from 1/8th of a second up to 2 minutes duration. Shorter duration gerbs are sometimes called Jets.

Gerbs are a pressed item. Loose composition is pressed inside to create a solid pellet of composition. A clay choke is either pressed or molded into the end of the tube, this choke produces back pressure which gives a gerb its shape and height.

The gerb is lit through the hole in the choke unless its duration is 1 second or less, in which case the speed of the burn means the composition can be lit from a hole in the centre of the gerb.

Long duration gerbs are pressed in stages, the tube with the choke is placed in a receptacle in the press and the tube is filled with composition form the bottom (it is the top because it is loaded upside down). When the tube is filled with loose composition, a ram is pressed inside the tube compressing the composition into a pellet inside the tube, the ram is extracted and the process is repeated until the final press where a clay composition is pressed to form an end plug/

When gerbs are pressed, the press is usually loaded with about 50 effects, this makes the slow process economically viable. only large gerbs are pressed singly.

The main ingredient in a gerb is usually meal powder, which is the fine dust that is left over when creating black powder. Black powder can also be used but it needs to be milled down to a fine powder to be useful.

An important point to note here is that metal does burn!, not great big lumps of it, but smaller particles are easily lit and burn brightly.

Titanium, Aluminium or Iron is usually added to the composition and these are the sparks which are seen. The metals are very fine particles or small flakes. The size of the particles depends on the height of the gerb, for example if you have a large metal particle that will burn for a long time in a gerb that only reaches 1 meter, the particle will still be burning when it reaches the apex of its flight and falls to the ground.

Gerbs don’t explode because they are pressed, black powder only explodes because the fire travels through the airspace and consumes all of the powder granules very quickly - this means the surface area that is available to the fire is massive because all of the granules are exposed to the fire. When you press the powder, you remove the air and create a pellet, when this is inside the tube, the only surface area available for the fire to consume is the top of the pellet, as it burns it exposes more composition to burn, pressing the powder slows the speed of the burn down

 

 

Flash

A simple device that creates an instantaneous flash when fired. There are variations to the simple flash, for example the flash can be coloured, or have a bang or have sparks added.

A flash contains flash powder which is quite a nasty substance, different formulas of flash powder can produce different effects. You can create a type of flash powder that detonates like high explosives.

A flash effect can be in various containers, including plastic pots, cardboard tubes, plastic bags, cling film or sometimes the powder can be loaded into metal flash pots directly.

 

 

Mine

A mine is an effect that shoots coloured stars up into the air. The effect is loaded into a tube which acts like a barrel to help project the burning stars up into the air.

The effect is in 2 parts, you have a lift charge which generates fire and gasses, the fire and gasses then light stars which are on top of the lift charge and the hot gasses from the burning lift shoot the burning stars out of the tube.

Producing good quality stars is the key to a good mine, they should have consistency, have good colour, be as smokeless as possible and create as little ash as possible. Different manufacturers create stars in different ways including, Rolling, Molding, Extruding, pressing. There are other methods, but the goal is the same, create uniformed small pellets of pyrotechnic composition.

Colour is important, unfortunately the stronger the colour the more ash is usually left, this ash will always fall out and is very uncomfortable if it goes in someone’s eye. it also can fall on some very expensive equipment like band and camera equipment.

Speed of burn is also important, if a star burns too long, it risks reaching the apex of flight and falling back down burning, and if a star is to quick, it will burn itself out too early and wont reach the height it is supposed to.

 

Maroon

A maroon is a device that explodes, as it explodes it creates a loud bang. Maroons can be made from plastic or cardboard. Plastic maroons tend to be more violent as the casing is stronger and gives better compression. The composition inside a maroon is a variant of flash powder. The casing is sealed to create compression and the explosion is due to the casing busting from the tremendous pressures inside the device.

Maroons are one of the most dangerous devices available, as they explode fragments of the casing (shrapnel) are projected with great force and can seriously injure people. Many manufacturers recommend that maroons should only be used inside a bomb tank which is designed to capture the debris.

Maroons are available in various sizes from ultra miniature which are used as bullet hit simulators through to ground maroons which are used for battlefield simulation.

Maroons are often used in film and television to make props explode.

   

 

Concussion

Concussion is a very potent form of flash powder. The powder is loaded into a concussion mortar (or Concussion pot) and when fired it creates a very loud bang. Concussion effects are usually fired in conjunction with other effects to give a jarring shock with the visuals.

Extreme caution should be used with concussion effects as the volumes involved can easily damage hearing. Because of the danger associated with concussion, many companies suspend the concussion pots from the roof of a venue so that it is out of the way of everyone. Flying the effect also has the added benefit of increasing the delay of the reflection of the pressure wave, if the effect is stood on the ground, the ground will amplify the pressure wave considerably.

The phrase that is used to determine the pressure wave is Air Over-Pressure, Air over pressure is measured in Linear decibels (dB(L)). it is widely agreed that 140 dB(L) is the level at which hearing damage can occur. In the UK 138 dB(L) is the peak exposure limit set out in the new noise at work regulations. It is VERY easy to exceed 140 dB(L) even with one or 2 grams of concussion powder, hence it is becoming more difficult to use concussion these days.

 

Flame Projector

Flame projectors are stunning hot and bright effects that are very popular. They are simply a tube containing nitrocellulose granules. These granules are the same that are in shot gun cartridges, in some countries you can buy it and it is usually called green dot.

Flames usually do not contain more than 250g of powder. There is a very small percentage of nitro glycerine in some makes of flame powder and if used incorrectly the powder can explode with devastating effect, this is usually why greater volumes are not used.

Flame powder must be lit from the top of the powder level otherwise the slow burning powder can shoot un burnt powder form the tube and it will be wasted.

The normal colour of a standard flame is orange, however you can add an additive that will change the colour of the effect - usually red or green. Care should be taken when using coloured flame projectors and the additive contains a chlorine donor that produces irritating noxious gasses that will make an audience cough and gag.

 

Comet

A comet is similar to ma mine, but instead of having many stars there is only one, A single star of composition is fired up out of a tube that then burns itself out at the apex of its flight. The comet can also have metal flakes in its composition which will give a silver tail as the star rises.

The lift is usually produced by black powder. I have seen comets that have been lifted with flash, but the flash blinds you and you miss the star! Flash also lifts the star too quickly.

 

Airburst

An airbust is a small package of powder that is suspended in the air from its igniter wire. When fired the effect explodes in the air like mini firework shells and there is no debris to come back to the ground.

Airbursts used to be made by the operator but in recent years pre made airbursts have been made, theses are sometimes called RTG airbursts, RTG means Ready To Go!

It is important to make the airburst from materials that are not flammable seeing as they are usually suspended above peoples heads. Normal cling film should not be used because it is PVC based and burns and drips.

Traditionally Saran Wrap has been used because it is a microwavable type of cling film and is not PVC based. when burnt saran turns into a very fine black powder. if in the UK tesco microwave cling film is a good substitute for Saran wrap.

Some airburst's are made with small stars inside them, these do give the look of firework shells indoors, care should be taken with these effects because they are usually much larger and not suitable for small venues.

 

Waterfall

A waterfall is simply a gerb that is designed to be fired upside down. Sometimes these gerbs have no choke or a choke with a wide hole to lessen the pressure and make the sparks fall slowly and without force.

A major problem with waterfalls is that after the effect is spent, there can some times be a gas after burn, this after burn licks up the side of the cardboard tube and can set it on fire easily.

You can stop the tubes from burning by spraying them with a flame proofing solution before rigging them.

 

Spark Producing Device

Spark Producing Devices are also known as SPD's, Electric Fault Simulators, Robotics or Spark hits. They can be made form various compositions and be made in to many different packages. The simplest is a flash composition with metal flakes, these are used to simulate faults in electrical equipment such as fuse boxes. Other compositions may use zirconium, magnesium or aluminium.

Some SPD's are simply igniters that have been dipped in a composition. some manufacturers igniters give a nice spark in themselves and are good enough for some applications. SPD's are pressed like a gerb with no choke, these give a dripping effect that is sometimes used in TV and film to give a short circuiting cable effect or welding / metal cutting effect.

 

Ice Fountain

An ice fountain is one of the safest effects around, it has many the same characteristics of a gerb, but the main ingredient is a nitrocellulose floss in which the metal flakes are mixed in. as the composition is nitrocellulose, the temperature is much lower than a conventional gerb, this means that you can waft your hand through an ice fountain without getting burnt.

Because of this low temperature and safety of the effect, ice fountain are often put on cakes as a replacement for candles or just lately put into the centre piece of banqueting tables.

Ice fountains are usually available in various colours because nitrocellulose is easy to colour with various salts.

 

Smoke

Pyrotechnic smokes are special because it is the only way you can colour smoke. In dong so you add a heavy industrial dye to a pyrotechnic smoke composition, when lit, the hot smoke can easily dye anything it comes into contact with, however this is only likely to happen when the smoke is red hot, after it has exited the cartridge, it rapidly cools and the risk of staining is significantly reduced.

Smokes are usually quite expensive because the chlorate used in the manufacture is incompatible with sulphur. This means that a press will have to be totally cleaned to remove all traces of black powder before a smoke mix can be used, The cleaning also has to take place after the smoke composition has been pressed as well! This cleaning process can easily take a press out of production for up to a day. Some factories build separate buildings where chlorates can be used without risk of contamination.

 

Flare

A flare is a device that produces a very intense bright light of various colours. They are usually made by pressing flash powder in to a tube much like a gerb. Because of the flash based composition the effect is usually accompanied by vast amounts of smoke, this smoke usually helps to diffuse the bright light therefore enhancing the effect.

The light from a pyrotechnic flare is intense and the colour is very vivid, the light is unique and cannot be replicated by conventional lighting.

 

Fireball

Fireballs are a simple effect, they are usually made by placing a black powder lift charge in the bottom of a stubby wide cardboard tube, then on top of the black powder a substance that when powderised will burn like fire.

Usually this is lycopodium powder but cheaper versions are starch based and some are made of cremora or coffee whitener with a high fat content.

After fired there is usually a load of un burnt lyco or starch around the effect, this is powder that was not consumed by the fire. Usually about 90 percent of the powder will be consumed.

 

Mortar Hit

A mortar hit is the closest thing to an explosion on a stage, when fired they produce a hot bright fireball with a bang and lots of smoke.

They are made in a stubby cardboard tube with a black powder lift charge in the bottom and on top of the lift a composition is suspended ready to be dispersed and lit. the composition is bright and hot and sometimes is a hexamine based composition.

 

Flash Tube

A flash tube is also called a split mine. it is a tube which has been cut down the side to create a slit the entire length of the tube. The tube is plugged at one end and filled with a composition that can simply be a flash mix or a flash mix with coloured stars.

When full another end plug is installed and a plastic tape is usually put over the slit to stop the contents from escaping.

The effect is fired on its side with the slit facing upwards. When fired, the effect is ejected along the length of the tube. The effect can be very messy and unpredictable, this is why they are not used much anymore.

 

Line Rocket

A Line rocket is a device that is attached to a steel line and allowed to travel the distance for the line. Line rockets are usually just whistles because they produce lots of thrust, sometimes they have metal flakes pressed in to the composition to create a comet tail of sparks behind it.

Line rockets usually travel very fast, but it is a great effect that can safely be shot over people’s heads.

 

Whistle

A whistle is a device that produces a shrill noise, it is made from a composition that is designed to produce large amounts of gas, as these gasses exit the tube, they produce a whistling noise. The tone of the whistle usually changes as the composition is consumes and the burning part moves further away from the mouth of the tube.

 

Crossette

A crossette is a very hard effect to make, it is essentially a comet that rises and then splits into 4 parts that creates across shape in the sky. Crossette’s are spectacular when they work but when they fail they have the potential to seriously injure people, this is why Crossette’s are not made by all pyro companies.

 

Saxon

A saxon is a spinning gerb, it is secured with a nail through the centre of the device. The choke is angled at either 45 or 90 degrees to allow the sparks and thrust to exit from the side and therefore make it spin. Saxons are often coloured and there are variants that have 2 gerbs so when one is finished, the other one lights and can spin the opposite way.

 

Bullet Hit

These are ultra small and flat devices that are used to simulate bullet hits on people, walls and objects. Sometimes they are miniature maroons, but the most common and by far the best are the "D" Range from De La Mare. They are sometimes called aspro dets because they resemble an aspirin. "D"s are available in various sizes and have 1 thin enamelled wires form the device for easy concealment.

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Firing Methods and Systems

There are many different systems in use today that are designed to fire pyrotechnics. There are simple hand held one shot systems right through to digital computer controlled systems designed to fire spectacular rapid chase sequences.

Many pyrotechnic operators use home made controllers, this should strongly be avoided and a commercially made controller form a recognised company should be used. The reasons you should not use a home made controller are:

  • Insurance - If you have an accident, using a home made pyro controller will not go in your favour.
  • Safety - Things do go wrong inside home made controllers, recognised manufacturers will have product liability insurance to cover this.
  • Inspections - It is unlikely that a home made controller will pass a local authority inspection.
  • Expertise - there are certain technical issues you may not be aware of, such as the fact certain pyrotechnic igniters short circuit in approximately 5% of cases, a load should be placed in line to avoid short circuiting the power supply.

 

Direct battery connection

You can fire a pyro directly from a battery or power supply. When firing effects from a battery you should be aware of the fact that each igniter can draw up to an amp of power,. If you are firing using a pp3 9volt battery, you will only get a few shots form the battery before it is exhausted. you can use sealed lead acid or gel cell batteries and they will be able to supply height current in bug bursts.

 

Capacitor Discharge Firing systems

Most commercial firing systems use this method, there is either a capacitor storing a charge direct from a battery or there is circuitry that generates High voltage and then the high voltage is stored as high energy and discharged into the firing lines - this method is very similar to the cay a camera flash strobe works, the energy is drained form the battery over a relatively long time, stored then released all at once, this allows the battery to drain at a slower more controlled rate which is needed in batteries like PP3's which have a relatively high internal resistance.

 

Digital Firing Systems

Digital firing systems are the way of the future, they offer a better way of working with pyrotechnics including:

  • Expandable Channels
  • Simple Daisy Chained Wiring
  • Computer controlled firing

If managed well, it is possible to create a large scaled pyro display without the use of any bell/speaker wire, this means considerable time savings on site.

Digital controllers have a main controller and modules that are connected by a cable network, modules are addressable and power and data are delivered down a single cable. Most digital controllers have a separate computer program that allows you to choreograph the show beforehand and print a show / loading report which is easy for the technicians to follow.

When the show has been agreed and planned beforehand, it is then possible to build the show on boards, load and wire them before you get on site, this makes the installation and de rig very quick indeed.

Digital firing systems do have a drawbacks, the system needs to be told what to do in advance, on a conventional controller you have the option of selecting or deselecting any channel at the time of firing. Making changes to a digital show can be time consuming, but an experienced operator with the laptop besides the controller and plugged in can chang masses amounts of data in a very short space of time and then download the new show in seconds. Another problem with digital systems is the cost, they are prohibitively expensive

Another benefit to the digital systems is that you can store many shows for any eventuality, so lets say you were doing a firework display and the wind was too strong, you can load a show that has omitted all long burning fireworks form the show that could cause a problem. If this was a hard wired sequence controlled display, someone would have to manually find and disable the effects.

Digital firing systems:

  • Pyrodigital
  • Fireone
  • FireCTRL
  • Pyromate Smartfire and Digital Nighthawk

 

Wireless

There are now some very special well made wireless firing systems available and the prices are dropping all of the time. Just recently a market leader has developed a 2 way wireless system that allows two way communication to the desk so that continuity and other functions can be done from the controller.

All wireless firing systems should use a high level of encryption to operate safely. normally this is done using a data burst that contains a long "key" along with channel data. A chip in the receiver will read the key and only fire if it receives a valid key.

Some controllers transmit the key up to 10 times, and the receiver has to receive at least 5 unbroken transmissions, it later became apparent that there was then too much security in the system that it stopped functioning reliably, so this value was dropped to 2 uninterrupted transmissions.

Wireless firing systems usually operate on a public licence free band that only permits short transmissions, in the UK this is usually 433Mhz which is a popular and widely used frequency for low power short duration transmissions (for example car lock key fobs).

If a fire signal is sent at the same time that someone in range transmits his key fob, the system still has a high possibility of working because it is more than likely the pyro transmitter will be more powerful and will "break through" the other transmission. if however the system does get confused, it should simply jam and will not fire. In reality, this very rarely happens, I have installed wireless equipment on many long running shows with great success and have never had any reports of jamming.

Wireless systems:

  • Galaxis
  • Le Maitre
  • Pyromate

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Wiring Pyrotechnics
Direct Channel to Effect Connection

The most obvious wiring method is direct connection, this is simply where a cable is placed between one effect and one output on the controller, this gives the user the most flexibility because the operator has the option of de selecting any of the effects from the firing sequence.

The disadvantages are that this method requires a lot of cable to be run and most controllers are very limited to the amount of channels they have available.

 

Parallel Connection

Wiring pyrotechnics in parallel is the most common way of wiring pyrotechnics because it is relatively straightforward and easy to understand. Each pyro connection requires 2 connections, much the same as a battery has positive and negative and the mains has live and neutral.

The output from the controller goes into the first effect and then from the first effect on to the next and so on. This method is capable of firing fewer igniters than series (depending on the type of controller) because a bunch of paralleled igniters will require significantly more current to fire.

The main drawback with this method is the testing procedure. When the controller tests a pyrotechnic circuit it essentially performs a continuity check. With parallel circuits only one effect in the circuit needs to be correctly wired and functioning properly for a pass to be given. As an example you have a circuit of 10 effects and 5 of them have been incorrectly wired and 5 of them are fine, when you test the circuit you see the test LED light to give you a pass. When you press the fire button only the 5 correctly wired effects will fire.

 

Series Connection

Series wiring is slightly more complicated but the preferred method. When you make a series circuit you essentially create one big loop and splice the pyrotechnics into the loop.

The disadvantages are that your circuit is vulnerable, if you have a cross fire and one of the effects is spent, the loop will have been broken and none of the effects will fire. This sounds unacceptable but in reality it very rarely happens and there are ways you can protect pyrotechnics from cross firing.

The biggest advantage with series wiring is that when you have a pass test LED, the test current is passing through all of the effects in the circuit, if one of the effects is malfunctioning or incorrectly wired, the fault is immediately visible to the operator who can then investigate the problem. You can also use a multi meter on the circuit to check you have the correct resistance.

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High Explosives

First things first, HE is very dangerous - that is why terrorists and the military use it but it does have a useful side as well as a destructive side - in fact it is that destructiveness that is useful. our civilisation would not have made the leaps forward it has done if it were not for the invention of explosives.

Explosives are simply a substance that contains vast amounts of potential energy that is able to be released quickly. Explosives fall under 2 categories, low and high, there is a further classification of Deflagrating or detonating, deflagrating means "Burns Rapidly", where detonation is a much more powerful phenomenon

Explosives detonation is measured in meters per second, we call this reading VOD or Velocity Of Detonation - that is the speed at which the shockwave travels through the substance, the higher the VOD the more powerful and destructive the explosive is. The threshold of low to high explosives is 1000 meters per second

To initiate High Explosive you need to use a detonator

There are several types of explosives including:

Explosive Velocity Of Detonation
Black Powder  
Flash Powder  
ANFO  
Nitroglycerine 7700 (Dynamite is slower)
TNT 6900
PETN 8400
RDX 8750
Nitrocellulose  
Slurry  
Emulsion  
HMX 9100

 

There are also many other substances that have been created, but the above are the most widely used explosives.

The above explosives are the main ingredient of explosive products, below are some of the most commonly used explosive products.

Detonators

Detonators explode at tremendous speeds, they are the most dangerous part of High Explosives as they contain many compositions that burn through stages. First is usually lead Azide which is a very sensitive composition and a small spark will set it off, this then goes through various compositions that at each stage detonate faster until it reaches the final stage which then transfers to the explosive being used.

Detonators are called Primary Explosives because they are the first stage of ignition, all other explosives are secondary. The usual detonator used for most applications are called No8.

Detonators can be electrically fired or use non electric systems.

 

Boosters

Some explosives require a faster detonation wave than a detonator can supply. Explosives like slurry type explosives are what is called Detonator insensitive, this means the detonator needs a booster to initiate the slurry. A typical booster is made from PETN which will increase the vod to 8400 m/s.

 

Detonating Cord

Detonating cord is one of the most versatile products available. It looks like washing line with a powdered core. The powder is PETN and because it is a cord, it can be shaped or wrapped around objects very easily. Detonating cord is available in various strengths that is measured in grams per meter. Detonating cord is detonator sensitive so no booster is needed to initiate it.

 

Dynamite

Dynamite is usually Nitroglycerine stabilised in clay, Dynamite has a relatively slow vod so is perfect for moving large objects because it does less damage and expands into large volumes of gas. Dynamite is often used as a lifter for petrol bangs, however because there is only detonation and no flame, the vaporised petrol does not light unless you use a slower flash powder device as well.

 

Semtex / PE4

Semtex and PE4 are plastic explosives, they are essentially RDX or PETN suspended inside a polymer plasticiser. The vod of these explosives is very high and they are quite pokey substances. They can be shaped to focus the energy of the blast very easy which makes them ideal explosives for cutting or blasting precise holes.

 

Slurry

Slurry explosives are great lifting charges as they produce vast amounts of gas as they detonate. They are perfect for simulating bomb hits where large volumes of earth need to be moved. Most slurry explosives are detonator insensitive so a booster is needed.

 

Shaped Charge

Shaped charges are perfect for blasting holes with precision. as an example if you need a tyre to blow out on a car a shaped charge will blast a hole in the wall of a tyre with ease guaranteeing a blowout every time. Shaped charges are very easy to make with plastic explosives

Linear Cutting Charge

Perfect for instantly cutting through anything - I mean anything. You can cut a doorway in a brick wall in a fraction of a second. on a more practical note, smaller linear cutting charges are very useful for cutting supports and chains.

Linear cutting charges are simply shaped charges but in lengths instead of round.

A perfect example would be that a giant film set need to look like it is collapsing. Carefully positioned cutting charged on the supporting steel work will make the whole thing collapse on cue. There are many commercially available cutting charges on the market, but it is very easy to make a linear cutting charge, below is a home made cutting charge made from plastic conduit

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