02Feb 22

Sustainability

Critics have long claimed that firework displays are just money going up in smoke, but this view seems to be gaining more traction now that the world is focused on the harm caused by greenhouse gases.

So abandoning fireworks should be a no-brainer – an easy way to reduce CO2 emissions. Certainly fireworks are never going to be 100% green, but provided you believe that a net-zero future should still include some fun and entertainment, the case against fireworks may not be quite as ironclad as it seems. Let’s take a closer look.

Carbon Emissions from Fireworks

The main explosive content of fireworks is gunpowder (black powder), which is a mixture of sulphur, saltpetre (potassium nitrate) and charcoal.

Like all explosives gunpowder carries its own oxygen (in the saltpetre) which is why burning gunpowder is so difficult to extinguish. But this also means that when burned, 1kg of gunpowder produces just 0.5kg of Carbon as CO2 and CO. By comparison 1kg of diesel fuel (which has to take oxygen from the atmosphere as it burns) produces 3.1kg of CO2 (petrol produces a fraction less than this).

In addition, the carbon in gunpowder is charcoal, which is made from wood rather than fossil fuels and has the potential to be sustainable, depending on the method of manufacture.

To put this in context, a moderately-sized display would have a Net Explosive Quantity (NEQ) of 50kg of gunpowder – the CO2emissions this generates would be equivalent to using about 9.5 litres of diesel, which would take the average car about 200km. And of course, the firework display will be enjoyed by hundreds or thousands of people, whereas the car will carry only five.

There’s more detail about how these figures were calculated in the Appendix.

Other Combustion Products

Fireworks produce a lot of other products when they burn, which come from both the black powder and the much smaller amounts of other chemicals used to produce the various effects (colours, bright flashes, loud reports etc.). Here’s a summary from our 50kg display:

Carbon output (as CO2/CO) 25.00 kg

Nitrogen oxides (NOx) 2.00kg

Sulphur dioxide (SO2) 1.00kg

Total solids 24.00kg

Of which

Total solids (insoluble) 5.50kg

Only insoluble by-products are considered to pose health risks for inhalation

PM10 (insoluble) 0.55kg

PM2.5 (insoluble) 0.28kg

The solid by-products are mainly potassium salts (black powder is 75% potassium nitrate) and aluminium oxide (aluminium is added to produce bright silver sparks).

The quantity of fine particulates produced (PM10 and PM2.5) is comparatively small, and these will be distributed throughout a large volume of air and well away from any spectators or bystanders.

Waste and Recycling

What about the rest of the materials in fireworks? Anyone who has ever handled any knows that there’s much more to fireworks than just gunpowder. The total weight of the fireworks in our example show with 50kg NEQ will actually be almost 300kg!

Most fireworks are constructed from cardboard tubes plugged at one end with clay: the cardboard used is itself often recycled material. Both these materials degrade quickly and harmlessly, but the cardboard can also be recycled by specialist companies: all waste from Fantastic Fireworks displays is returned to our site after the show and sent for recycling.

Unfortunately domestic waste recycling does not handle fireworks at present, so councils advise that used consumer fireworks should be soaked in water for 20 minutes before bagging them and putting them in the general rubbish bin.

Plastics

Most fireworks already contain comparatively small amounts of plastic, and manufacturers are working to reduce this amount all the time.

The exceptions are specialised single-shot mines (typically used for low-fallout and close proximity displays in stadiums etc.) and some European-manufactured aerial shells and rockets.

Single shot mines may have plastic bodies: these remain in place after firing so they are easily collected for recycling.

The plastic waste from aerial shells and rockets can’t really be collected up after a display, so Fantastic Fireworks does not use these fireworks in any of our displays.

Appendix

Emissions produced by black powder

CarnDu Ltd has developed an Environmental Calculator for firework displays that produces a detailed analysis of the environmental impact of a display. As well as calculating the immediate products of combustion, this calculator can estimate the carbon footprint of all aspects of the display from manufacture and transportation through to disposal of the spent fireworks. This calculator has been used to produce all the numbers in this document.

Nevertheless, it’s helpful to get a feel for the figures by digging a little way into the chemistry of the combustion of fireworks. What follows is a simple analysis using three different methods.

Complete combustion to gases

Black powder Formulations vary depending on the application, but a common recipe is 75% potassium nitrate, 10% sulphur, 15% carbon (by weight).

Molecular weights:

Oxygen = 16g

Carbon = 12g

Sulphur = 32g

Nitrogen = 14g

Potassium = 39g

Potassium Nitrate (KNO3) 39 + 14 + 3×12 = 101g

1kg of gunpowder contains 150 g (12.5 moles) of carbon, producing (12+32)x12.5 = 550g of CO2. It contains 100g (3.125 moles) of sulphur, producing (32+32)×3.125 = 200g of SO2

And 750g (7.43 moles) of KNO3 – – hence 7.43 moles of nitrogen – producing (14+32)×7.43 = 341.6g of NO2

550g / kg CO2

200g / kg SO2

342g / kg NO2

Incomplete combustion

But apparently gunpowder doesn’t burn completely to gas: there are many solid combustion products. An approximate formula for combustion is

10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2.

(Notice that no sulphur dioxide or nitrous oxide is produced)

10×101 + 3×32 + 8×12 = 1,202g gunpowder produces 6×44 = 264 g CO2

264/1.202 = 220g / kg CO2

Alternative formula for incomplete combustion

An alternative combustion formula is:

2 KNO3 + S + 3 C → K2S + N2 + 3 CO2

(Again notice that no sulphur dioxide or nitrous oxide is produced)

2×101 + 32 + 3×12 = 270g gunpowder produces 3×44 = 132g CO2

132/0.270 = 489g / kg C02

Comparison with Petrol / Diesel

Combustion of diesel fuel produces 2.68kg C02 / litre, (petrol 2.31kg / litre)

In our calculations above, we see gunpowder generating between 220g and 489g CO2 / kg. Taking the larger value (which is not far from the “complete combustion” value), we can see that 1kg of gunpowder emits the same amount of CO2 as:

0.49/2.68 = 0.18 litres of diesel.

So a typical small display with 30kg NEQ generates the same CO2 emissions as 5.5 litres of diesel. This is the equivalent of driving an average car about 120km

(The average emissions for new cars sold in 2017 were 120g CO2 / km)

A very large display like the British Fireworks Championships in Plymouth with 500kg NEQ would be equivalent to driving an average car about just over 2,000km – but the Plymouth displays are watched by over 200,000 people!