Seven hours after two vessels collided in the Houston Ship Channel this month, causing a massive spill of a gasoline blend with high concentrations of benzene, a state contractor detected levels of the cancer-causing chemical that exceeded the state’s threshold for short-term exposure.

In fact, some Seabrook residents could have been exposed to levels of benzene 14 times higher than the point at which state officials consider it a cause for worry.

Yet, no one was notified for hours.

The lapse in communication is a symptom of a system that fails to inform communities when they are potentially exposed to dangerous chemicals, critics say. Some believe the Texas Commission on Environmental Quality could be doing more.

“I’m questioning what, if any, measure the agency is taking to ensure that public health is being considered as they are recording these measurements,” said Elena Craft, an air quality expert with the Environmental Defense Fund. “I can’t emphasize how extraordinarily high they are.”

But state environmental officials said they followed procedure and notified a unified command that was responding to the incident. For various reasons, a social media alert did not go out until the following day.

The May 10 collision occurred when a 755-foot tanker carrying liquefied natural gas struck a tug boat pushing two barges. One barge capsized and the other was damaged, leaking more than 11,000 barrels of a gasoline blend product called reformate, a highly flammable chemical that’s mixed with gasoline.

At 10:30 p.m., a contractor hired by TCEQ detected 2,400 to 2,600 parts per billion of benzene at the intersection of Todville Road and Brummer Hop in Seabrook . According to the state agency, short-term exposure — up to one hour — of benzene concentrations above 180 parts per billion can be a cause for health concern.

Less than an hour after the initial reading, at 11:20 p.m. on May 10, no benzene or other volatile organic compounds were detected, according to the state agency’s online update.

TCEQ was assisting with air monitoring and, based on its protocol, provided the readings to the unified command “so agencies with lead jurisdiction could make decisions about issuing advisories to the public, as warranted.” said Andrew Keese, a spokesman for the state agency.

Craig Kartye, a member of the unified command and the Texas General Land Office, said they learned about the high readings two hours after they were taken. Neither the command’s air-monitoring contractor nor Harris County Pollution Control, which also was testing air quality, detected benzene readings at those levels. “We had so many teams in so many areas and none of the other teams were able to see that reading again,” he said.

Keese said the unified command was not notified sooner because it had not yet established a communication protocol through an on-scene coordinator when the high level of benzene was detected and that “as soon as the communication channel was identified, the readings were provided.”

TCEQ posted an alert on social media at 1:17 p.m. May 11, nearly 15 hours after recording the elevated reading.

“High levels of benzene and other volatile organic compounds were monitored in the area soon after a collision involving barges in the Houston Ship Channel on May 10,” the alert stated. “Monitored levels in the area since then are lower, but still elevated. While not a long-term health concern, short-term exposures to these elevated levels can cause headache, nausea, and eye irritation. People who smell the gasoline-like odors may want to avoid the area out of an abundance of caution if they experience these transient effects.”

The agency also recorded elevated benzene readings of 200 parts per billion in Kemah and 400 parts per billion in Bacliff, not nearly as high as the one in Seabrook.

Gayle Cook, Seabrook city manager, said local officials were in contact with the unified command, but they weren’t getting real-time monitoring data and didn’t receive the TCEQ readings. She declined further comment.

Benzene is made mostly from petroleum and is used to produce Styrofoam, synthetic fibers, rubbers and pesticides, among other substances. Vehicle exhaust accounts for the largest source of benzene in the general environment.

Risks of benzene exposure can vary depending on the concentration and time of exposure. While short-term health effects include dizziness and headaches, continuing exposure can affect the bone marrow and lead to a condition known as aplastic anemia.

Although it is not known how long the high reading lasted, “that level of exposure for up to one hour is not acceptable,” said Dr. Arch Carson, associate professor of environmental and occupational health sciences at the University of Texas Health Science Center in Houston.

“It would be considered an overt exposure and could result in health effects probably not apparent immediately, but could add significantly to things like the risk of leukemia,” he said. “Although the risk was very small in this case, clearly it was not zero.”

“In an environment where I don’t know what’s coming behind that reading and it’s a community setting, I would recommend shelter in place and suggest it be broadcast across the emergency notification network,” he added. “Until you know what the actual situation is, that is best practice in terms of good precaution.”

Two months earlier, a shelter-in-place order was issued as a precaution during the Intercontinental Terminals Co. facility fire in Deer Park after a single benzene reading lower that what was detected in Seabrook, she said. On March 21, four days after tanks in the chemical holding plant caught fire, TCEQ posted that one-hour levels of benzene in Deer Park were measured at a maximum of 190.68 parts per billion at 4 a.m., dropping to 48.03 parts per billion at 5 a.m.

“If it’s truly an instantaneous reading, why not take another sample five minutes later?” Craft asked.

Keese wrote in an email that the elevated readings “were taken in the overnight hours, and TCEQ contractors remained in the area for about 20 minutes and returned to the location within the hour to determine if the elevated readings persisted. There were no detections of monitored contaminants or odors.”

The area is still recovering from the ITC fire, Craft said, which a month later still showed high levels of benzene nearby.

“We are in a situation where we have repeated exceedances with contaminants that are known to have long-term health consequences,” she said. “Whether you are concerned for human health or the ecosystem health, we are part of one food chain.”

perla.trevizo@chron.com