Put simply, firework displays are not risk free. It is, of course, vital that the risks are carefully assessed and managed and are as low as possible – under the conditions that display will be fired. The process of managing the risks involves all parties – the event organiser, the event producer, the enforcing authorities and the firework contractor – and requires a sound comprehension of the various risks involved. In general the show must be designed to maximise the potential for firing under a variety of “most likely” and “worst case” scenarios. Careful consideration must also be given to what is achievable under a variety of meteorological conditions – the weather on the night of the display, especially in November or for New Year, is unlikely to be that during the pre-event site visits.

Shellcalc© is one tool to help this process – Shellcalc© is a sophisticated trajectory and fallout modelling program designed to run in Microsoft Excel©. For smaller individual display site and product specific modelling is probably not justified – but nevertheless Shellcalc© can be used to provide firers with sensible information about the products that they are firing and allow them to make informed decisions “on the night”. For very complex and high profile events extensive Shellcalc© modelling may be carried out to investigate the risks under a very wide range of conditions.

It is somewhat over 10 years since the first paper on Shellcalc© was published in the Journal of Pyrotechnics, although the program itself had been developed some time before by John Harradine in Australia following two firework incidents. This paper looks at the development and use of the Shellcalc© Pro program – a useful tool in the planning stage for any fireworks display company.

Two recent reviews (See Journal of Pyrotechnics Issue 33 (2014) pages 39-52 and 53-64) of “fixed rule” regimes for calculating “safety distances” confirm what most of us have known for many years – that most “safety distances” do not guarantee safety! Most fixed rule regimes do not adequately address wind speed and direction, differing firing angles and the consequences of low frequency but high hazard events such as shell “blinds”

From an event safety point of view a realistic appreciation of the risks is vital and the event organisers must be clear what level of risk is expected and is acceptable – there is almost no such thing as a totally “safe” show.

The original Shellcalc© program (see left) calculated the trajectory and burst point of a shell or comet and gave both numerical and graphical output.

The data produced was useful but limited (as it predominantly was used for modelling “blinds” and over the years, and following feedback from users and event organisers, we have developed the program significantly to incorporate both Low Frequency/High Hazard events (such as “blinds” and High Frequency/Low Hazard events (such as “normal” and “long burn” fallout)

Screen Shot 2015-05-26 at 21.08.24

Shellcalc© Standard (Version 5.23) is a free program which has enhanced the usefulness of the original by incorporating features such as:-

  •  Shell burst diameters
     “Normal” and “Long Burn” fallout
    Firing from above or below ground level (for structures or for firing between buildings)
    Firing above or below horizontal (useful for comets)

ShellCalc© Pro is a further significant development and which is available for purchase by subscription. ShellCalc© Pro (current version 7.30) offers the following new functionality:-

  •  Modelling 5 effects simultaneously
     Modelling Mines and Gerbs (and each effect is modelled 3 times – see later)
     Numerical input/output in Metric or imperial units
     Choice of windspeed inputs
     Multilingual support
     Independent x/y/z positioning of firing points
     User selection of all graphical display options


Screen Shot 2015-05-26 at 21.26.30Trajectory plot 

This plot shows the burst diameters and “normal” fallout from 3 shells

This plot is for the following
150mm shell fired vertically
100mm shell fired at 15°
100mm shell fired at 15° but offset by 100m
Force 4 – 45° wind angle

*Note long burn arrows are not shown

Screen Shot 2015-05-26 at 21.26.48Ground Track 

This is for the same situation as above with “Long Burn” debris circles shown.
This plot is ideal for superimposing on maps or aerial photographs within the program




Screen Shot 2015-05-26 at 21.27.112 position firing comet plot 

This trajectory plot shows:-
2 x 30mm comets with 2 sec flight time
Fired 130m apart at 80° from vertical firing angle
Force 4 wind and 180° relative wind angle (ie from right to left)

This is useful for modelling, for instance, comets fired from a stadium roof

Screen Shot 2015-05-26 at 21.27.39Mines firing off structures 

This trajectory plot shows 3 types of mines fired 50m above ground and fired at 30°, 45° and 90° from the vertical (note mines are different calibres and spreads)

Mines (and Gerbs) are modelled independently as 3 separate projectiles to allow for wind effects to be modelled (for instance with long burn effects)

Shellcalc© Pro now allows users to incorporate maps or aerial images into the program itself – to allow immediate visualisation of debris and fallout as the input parameters change. The new version of the program was used to prepare contingency plans and selective removal of fireworks from the London New Year show in 2014 where debris effects were modelled in 8 different wind directions, each with 4 windspeeds.




The Shellcalc© Pro program is continually being developed and refined to incorporate new features and user feedback is welcome either directly, or via one of the Shellcalc© training workshops (see http://www.pyroworkshops.com). The Shellcalc© Standard program will not be developed further but will remain free to download and use.

ShellCalc© is now used by some of the largest display companies in the World and at some of the largest events, to make informed choices of materials to be fired (and to support site and product specific risk assessments) and to produce practical contingency plans for the curtailment or cancellation of displays. Shellcalc© is not a show simulation program, but can be used alongside such programs and a sound knowledge of the firing site and products to manage the risks of firework displays and to allow creative and spectacular displays to continue to be fired.

For more information and examples of a brief BBC documentary on the planning of the 2014 London New Year display and the use of Shellcalc© please see the following sites or contact the author direct.



Dr Tom Smith is chairman of the CBI Pyrotechnic Group (www.eig.org.uk ) and Secretary of the British Pyrotechnists Association (www.pyro.org.uk ). Tom is the Managing Director of CarnDu Limited (www.carndu.com ), an independent explosives consultancy, and has worked on some of the most major firework displays around the world. He is also the author of a recent textbook – Firework Displays: Explosive Entertainment (www.fd-ee.com ).