{"id":332,"date":"2011-06-15T19:30:30","date_gmt":"2011-06-15T18:30:30","guid":{"rendered":"http:\/\/www.pyro.org.uk\/?page_id=332"},"modified":"2025-05-26T19:40:05","modified_gmt":"2025-05-26T18:40:05","slug":"shellcalc","status":"publish","type":"page","link":"https:\/\/pyro.org.uk\/?page_id=332","title":{"rendered":"Shellcalc\u00a9"},"content":{"rendered":"

\"\"<\/a>
\nThis paper is adapated from the book “Firework Displays:Explosive Entertainment” by Dr Tom Smith (BPA Secretary) – details of the book and ordering information are available at http:\/\/www.fd-ee.com<\/a><\/strong><\/p>\n

Shellcalc \u00a9 has been adopted by the BPA and many other organisations around the World as the de facto<\/em> means of predicting shell and comet trajectories.  It does not address “normal” fallout but it can be used with other calculations to predict “normal” fallout from aerial fireworks.<\/strong><\/p>\n

Shellcalc\u00a9 <\/sup>is a tool developed by John Harradine(1) of Queensland, Australia following investigation into an incident at Bray Park and modified by the author of this book (2) which produces numerical and visual representations of shells and comets in flight for use in planning \u201csafety\u201d distances.<\/p>\n

Shellcalc\u00a9 Standard and Shellcalc\u00a9 Pro are available at www.shellcalc.co.uk<\/a> and www.facebook.com\/shellcalc<\/a><\/p>\n

The program, written in Microsoft\u00ae Excel for convenience, has been extensively modified and allows inputs as shown in the table below:<\/p>\n

Table \u2013 Shellcalc\u00a9 <\/sup>input parameters<\/em><\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Parameter<\/td>\nComments<\/td>\n<\/tr>\n<\/thead>\n
Type of effect<\/p>\n

 <\/p>\n

Shell or comet<\/td>\n

If \u201cShell\u201d is selected a burst diameter is calculated and a possible fallout trace is produced. If \u201cComet\u201d is selected then the projectile is assumed to be consumed during flight<\/td>\n<\/tr>\n
Units<\/td>\nMetric or Imperial<\/td>\n<\/tr>\n
Calibre<\/td>\nDiameter of projectile<\/td>\n<\/tr>\n
Mortar angle<\/td>\nDirection fired from vertical<\/td>\n<\/tr>\n
Muzzle velocity<\/td>\nEntered if known, otherwise standard values used<\/td>\n<\/tr>\n
Fuse delay<\/td>\nEntered if known, otherwise standard values used<\/td>\n<\/tr>\n
Shell mass<\/td>\nEntered if known, otherwise standard values used<\/td>\n<\/tr>\n
Tumbling\/mortar drift<\/td>\nAllows a factor to be introduced to simulate barrelling and tumbling effects.  If this is not present a shell fired vertically would land exactly where fired if no wind parameters are entered<\/td>\n<\/tr>\n
Wind speed<\/td>\nAt ground level<\/td>\n<\/tr>\n
Relative wind direction<\/td>\nRelative to the firing angle<\/td>\n<\/tr>\n
Elevation of launch site<\/td>\nTo allow for changes in atmospheric density etc<\/td>\n<\/tr>\n
Height of launch<\/td>\nHeight of launch point above the ground \u2013 introduced to allow for firing from buildings and to permit debris to extend below launch height<\/td>\n<\/tr>\n
Terrain category<\/td>\nTo accommodate open, wooded or built up areas.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Output from the calculations is produced graphically and in a tabulated form.  A selection of typical outputs is given below.  Note that the depiction of the shell burst diameter may be distorted depending on the axes that the program selects to display the results \u2013 the alternative would be a highly extended \u201cy\u201d axis in the majority of cases.<\/p>\n

Figure  \u2013  4\u201d (100mm) shell  \u2013  Fired 5 degrees from vertical with low wind<\/em><\/p>\n

\"\"<\/a><\/p>\n

Shellcalc\u00a9<\/sup> can also be used to model the trajectories of comets and this is particularly useful for the risk assessment of firing single shot items from buildings.  In this case Shellcalc\u00a9<\/sup> allows modelling of below horizontal firing and allows modelling of \u201cblow back\u201d onto the building in extreme conditions.<\/p>\n

Figure \u2013 Comet fired from a building<\/em><\/p>\n

\"\"<\/a><\/p>\n

Taken together the calculated data from \u201cnormal\u201d debris distances (which are relatively low hazard but high frequency) and shell failures (which are high hazard but low frequency) allow the display designer to design a display which presents an acceptably low risk, whilst also provides objective criteria for curtailment or cancellation of the display.<\/p>\n

We usually work on a normal maximum wind speed of Force 4 \u2013 this allows a display to be designed to accommodate the vast majority of conditions that would normally be encountered for displays.  If the wind is stronger than this then it is likely that other safety considerations will need to be considered anyway.<\/p>\n

Figure  \u2013  6\u201d (150mm) shell with deliberately extended fuse time (i.e. shell fuse failure) \u2013 note the position and extent of the predicted burst<\/em><\/p>\n

\"\"<\/a><\/p>\n

From all the data we have amassed and calculated, and with a knowledge of the material chosen for the display we usually then prepare an objective \u201ccontingency\u201d table for the display which details what curtailments will need to be made as a function of wind direction and strength.  Direction is important because it may be that from certain directions an additional risk is posed (i.e. towards the audience or other hazards) but if the wind is blowing in the opposite direction then a greater wind strength can be tolerated before curtailment or cancellation is necessary.<\/p>\n

\n
\n
\n

(1) J Harradine & T Smith, Journal of Pyrotechnics, 22, 2005, 9-15 \u2013  http:\/\/www.jpyro.com\/wp\/?p=23<\/a><\/p>\n<\/div>\n

\n

(2) See revised version of Shellcalc\u00a9 at  http:\/\/www.jpyro.com\/wp\/?p=1193<\/a><\/p>\n<\/div>\n<\/div>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

This paper is adapated from the book “Firework Displays:Explosive Entertainment” by Dr Tom Smith (BPA Secretary) – details of the book and ordering information are available at http:\/\/www.fd-ee.com Shellcalc \u00a9 has been adopted by the BPA and many other organisations around the World as the de facto means of predicting shell and comet trajectories.  It does […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":5195,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"https:\/\/pyro.org.uk\/index.php?rest_route=\/wp\/v2\/pages\/332"}],"collection":[{"href":"https:\/\/pyro.org.uk\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/pyro.org.uk\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/pyro.org.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/pyro.org.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=332"}],"version-history":[{"count":3,"href":"https:\/\/pyro.org.uk\/index.php?rest_route=\/wp\/v2\/pages\/332\/revisions"}],"predecessor-version":[{"id":12095,"href":"https:\/\/pyro.org.uk\/index.php?rest_route=\/wp\/v2\/pages\/332\/revisions\/12095"}],"up":[{"embeddable":true,"href":"https:\/\/pyro.org.uk\/index.php?rest_route=\/wp\/v2\/pages\/5195"}],"wp:attachment":[{"href":"https:\/\/pyro.org.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=332"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}