A brown and orange colored NOx cloud hovered over eastern Gillette Monday afternoon, prompting local emergency officials to caution anyone in the vicinity of the cloud to move inside and close all doors and windows.

Officials say the cloud is not poisonous, but warn long-term or repeated exposure can cause health effects.

“It’s not going to send you to the hospital, but if you did have compromised lungs – COPD or something like that – it would be something that could affect you more than somebody else,” explains Campbell County Emergency Management Coordinator David King.

Such clouds are a by-product of blasting, as ammonia nitrate is affected by moisture or blast-hole slumps.  The NOx cloud is produced when conditions are right at the time of the blast.