When a driver on the highway caught a whiff of the mist rolling across the road, he knew exactly what it was and called it in.
Emergency crews in Humboldt were called to an anhydrous ammonia leak eight miles west of Humboldt, at the Horizon Fertilizer tanks at Dixon, at about 4:30 a.m. on May 29.
A leaking valve was releasing anhydrous ammonia, a commonly used fertilizer, into the air. On the calm and very humid morning, it was hanging around in the air, but it was  drifting over to the nearby Hwy. 5, reported Humboldt Fire Chief Norbert LeBlanc.
“The smell was strong (on the highway),” LeBlanc said.
A driver on the highway had gone through the mist, and was able to identify it as anhydrous ammonia.
From the looks of it, the valve had been leaking for quite a while when firefighters arrived on scene to stop the leak, LeBlanc reported.
They donned their breathing gear and went in to turn the valve off.  They also called the owner of the tank to notify them of what had happened and asked them to come out to check things out.
Sometimes, LeBlanc explained, changes in temperature can expand the metal fittings on the valves, causing them to drip.
One drop of anhydrous ammonia expands to 800 times that in vapour.
One cubic foot of liquid, Leblanc said, equals 855 cubic feet of ammonia gas. And it vapourizes at any temperature warmer than -28ºC.
“When it hits the atmosphere, it evaporates into a cloud,” LeBlanc explained.
That cloud is attracted to water, which is why it is so dangerous to people.