The Blue Roman Candle is a small firework that fires a series of blue balls of light into the air to complement the more prominent boomers.
Facepunch implemented Fireworks into RUST during the Lunar New Year Update on January 24th, 2020.
Fireworks were available for a limited time through the Facepunch storefront but can now only acquire them through other players selling them on the Steam Marketplace.
Most players appreciate firework shows and understand that your base is unlikely to have much sulfur in stock by seeing your fireworks, making your base an undesirable raid target.
You can light your fireworks by individually striking each placed boomer by hitting it with a lit Torch, or you can set up an electrical firework Igniter that will set off all fireworks within a set radius.
Due to too many fireworks launching at once affecting lower-end systems, Facepunch implemented a limit on the number of fireworks launching at once. Servers now queue all active Firework launchers.