Plumes of silver or gold sparks of varying height and duration, shoot up to create a glittering effect.
The first number shows the burn time (in seconds) and the second number shows the height (in feet). The height is defined as the top of the main plume, some sparks will go higher. For example: a 3 x 20 is a gerb of 3 seconds duration that reaches a height of 20ft.
 
There may be minimal fallout as all pyrotechnics can produce some remnants of hot and/or cold fallout. Risk assessments must be carried out when using all Le Maitre products and this should involve a test firing of the product.