According to the Ngaosrivathanas, the nak "are known to control fire." Owning a piece of a nak crest is said to prevent fires. They add "A person with such a relic will be spared inferno. Chinese businessmen in Laos never miss placing such a relic in a glass of water in their factories." (Ngaosrivathana, 2009, p. 2)
Today, on many Wat Lao, you will spot ornamentation depicting nak on the eaves that are carved and decorated to prevent fires:
This isn't always 100% effective as recent fires in American Wat Lao have demonstrated, as well as during the razing of Wat Lao during the 1800s. But overall, it's been a tradition passed on for over 600 years and is part of the Lao heritage.