Using the 'Properties' tab in the Editor Panel, in the 'Event' sub-section, select either a sound, an effect, or a sound plus an effect to produce the explosion that you want. Click the 'Select' button next to the 'Sound' entry box, and look under 'Lifeless Unlooped' sounds. The example shown here is a fiery red explosion with black smoke, plus an added random 'heavy' explosion sound.
Use the 'Event impulse' properties to specify how often the effect is to occur. A fixed frequency can be specified, or a 'Random (sec)' interval, as shown in the example here. A spread of explosion events can be used in combination, each with a different random interval, to introduce variability into the sequence and timing of effects in each restarted game. This technique works well with odd numbers of seconds specified (in the example, 133 seconds is 2 mins 13 seconds). Try out different settings to achieve the best game effects balance, i.e. not too often / not too infrequent.
