Field Trip: Riding along with a motor fuels inspector

by | Mar 2, 2016

Most people pull up to the gas station about once a week to fill up their tank. Valerie Thoms, an inspector with the N.C. Department of Agriculture and Consumer Services, pulls her mobile inspection lab to the gas station about four times a day. But it’s not because she drives a gas guzzler. Her job is the check ethanol levels, octane readings and look for water and sediment at the gas pump.

“After your house, your car is most people’s biggest investment,” said Thoms. “My job is to make sure that consumers get the right product at the pump.”

After arriving at a station, Thoms uses Sargel, a water-finding paste, on the end of a long rod to check the gas tanks for water. The rod must be able to reach the bottom of the buried tanks that store the gas.

She then obtains samples at the pump of each grade of gas. After flushing about a half-gallon of gas from the pump, Thoms obtains two samples of each grade of gas. By law, each tank must have the grade, percent ethanol and name brand displayed, and Thoms checks to make sure the gas quality matches.

A visual inspection is first. She uses a flashlight to look for noticeable debris or sediment in the sample she has taken, then she takes the samples to her mobile lab space to check each one’s octane and ethanol levels. She also checks for cross-contamination with diesel or another fuel. (Click through the slideshow for visuals.)

Field inspector Valerie Thoms
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Octane levels are checked with a Zeltex machine, which is a fuel analyzer that uses infrared light to read the octane level of gasoline. If the reading does not match what is listed at the pump, Thoms will take the sample to the Motor Fuels Lab in Raleigh for further testing.

Ethanol levels are checked using a water strip test. Ten milliliters of water  is added to a 100-milliliter gas sample. Ethanol is water-sensitive and can be easily separated from gas. Thoms looks at the water line in the ethanol to get the percent ethanol added to the gas.

Finally, the gas sample is distilled to check for cross-contamination. After distilling, the residue must be less than 2 percent, and final boiling point less than 225 degrees Celsius, for the sample to pass.

Discovering and addressing problems

Problems at the pump are sometimes discovered. Some of these problems, such as water in the tank or sediment at the pump, may cause an inspector to shut down a gas station or pump at that station. Standards Division staff can close a station for phase separation, which is a mix of ethanol and water in the tank, if it is ethanol gas that is being sold at the station. Pumps can be shut down for sediment as well. Sediment must be coming through the pump for an inspector to take action on it. Almost every tank in North Carolina has some sediment in it, but the stations have filters on the pumps to protect the consumer.

“If I find a problem, the first thing we do is flush the lines at the station and retest the gas,” said Thoms. “If there is still a problem, the pump is shut down.”

Thoms can place a seal on the pump to keep it from being used until the station fixes the problem and gets another inspection. She tries to visit each station in her territory annually, and also checks stations that have generated consumer complaints.

“What we do at gas stations protects consumers and the business. The stations generally rely on their fuel company to provide the right product and don’t want to accidentally pass along something of inferior quality,” said Thoms. “Some cars require certain octane levels, and putting the wrong one in a vehicle could damage the car. Water in the gas tank could keep your car from even leaving the station, and cause hundreds of dollars in damage.”

As a consumer, it’s hard to tell if a station is selling a quality gas product. The good news is that at most stations, inspectors encounter very few problems. “A good rule of thumb is to pick a station with a clean, maintained yard area and a clean pump area,” said Thoms. “If the station keeps care of what you can see, then they most likely take care of what you can’t see too.” Also, print and keep your receipt when filling up your tank. This is proof of purchase if there is a problem.

In addition to checking fuel quality, Standards weights and measures inspectors also visit gas stations to test pumps to check that pumps are dispensing the right amount of gas. If you have a problem at a gas station with fuel quality or think you’ve been charged incorrectly, contact the Standards Division at 919-707-3225.