How emergency crews trace odd odors and determine if they're safe

HARRIS COUNTY, Texas (KTRK) -- Odd smells are no strange occurrence this close to chemical plants and the shipping port, but how is it determined where it's coming from and whether it's safe to be breathing in?

Richard Lawhorn with the Harris County Fire Marshal's Office said the hazmat team is one piece of a bigger puzzle when it comes to tracking down a mysterious odor.

"Basically, we're setting up areas to monitor and try to define where the source is coming from," Lawhorn said.

Lawhorn said a common odor the hazmat team responds to is most likely the same one people across Harris County were smelling Thursday. It's called mercaptan, a harmless chemical that is purposefully added to odorless natural gas so that a leak or spill can be detected.

Lawhorn said mercaptan is heavier than air, while natural gas is lighter, so the smell of rotten eggs or sulfur often lingers close to the ground, while the natural gas has already lifted and dissipated.

"You can smell the mercaptan, and there is not a hazard of natural gas there," Lawhorn said.

On Thursday, crews could not find the source of the smell and determined there was no danger. But how were they able to call it safe without knowing the source?

SEE ALSO: Channelview, Pasadena, Spring among areas of Harris County with reports of gas odor, officials say

Captain of Emergency Operations James Lanphear said when a smell is detected, they use several tools to track and trace it.

Computer models allow them to look at things like wind direction and speed to narrow down an origin, while handheld devices test the air over and over to find out what chemical is in the air and how much.

"What are the concentrations? How many more phone calls keep coming in? How many fire departments are responding? Is this continuing to travel on? And the other thing is basically we are not going to give up until we absolutely know there is no threat to public safety out there," Lawhorn explained.

When the air continues to test clean and the smell dissipates, Lawhorn said they pack up and rely on permanent air quality testers installed around the county to keep a final eye on the air.

Lawhorn said mercaptan can be smelled in very low amounts and can come from a tank being cleaned or opened. Thursday's windy conditions carried that smell across the county. Reports started in Channelview and progressed all the way to Tomball and Cypress.