By Collin Eaton and Erwin Seba

HOUSTON (Reuters) – U.S. investigators hope this week for the first time to enter the site of a massive fuel fire and chemical spill outside Houston to begin the hunt for a cause and to determine whether the operator followed safety regulations.

The blaze, at Mitsui & Co’s Intercontinental Terminals Co (ITC) storage facility in Deer Park, Texas, began March 17 and released toxic chemicals into the air and nearby waterways. Shipping along the largest oil port in the United States remained disrupted on Monday, as did operations at two nearby refineries.

Fumes from benzene-containing fuel and fear of another fire have prevented investigators from going into the tank farm’s “hot zone,” officials said Monday. Three tanks holding oils remain to be emptied this week, and responders continue to sop up fuels on the tank farm grounds.

Investigators from the U.S. Chemical Safety Board (CSB) and Environmental Protection Agency, as well as state and local authorities, plan to enter the site once it is safe.

Access to the site, along the Houston Ship Channel, will help determine what happened and how a fire at one tank holding tens of thousands of barrels of naphtha spread quickly to 10 other giant tanks.

“The escalation of the event, looking at how the fire spread from a single tank to others in the tank battery, is certainly something we’re interested in,” said CSB lead investigator Mark Wingard, who arrived in Houston last week.

Before CSB investigators enter the site, possibly later this week, they will focus on interviewing ITC personnel and witnesses of the fire, and collecting documentation on the facility and its tanks. The CSB’s investigation will also examine the “outside impacts” of the fires, Wingard said.

“There’s huge public interest in this case,” he said. “People in this community want to know what happened and what they were exposed to.”

Access also could provide officials with information critical to state and local lawsuits accusing the company of improperly releasing tons of volatile organic compounds into the surrounding air and water.

“We need to get to what was the root cause of this event and then begin to understand any aspect of negligence or obstruction that led to the event,” Harris County Commissioner Adrián García said in an interview.

The county last week filed a lawsuit against ITC seeking to recoup the costs of emergency responders and healthcare clinics set up in response to pollution from the fire. The county has not yet estimated the cost, which Garcia said is “going to be very significant.”

An ITC spokeswoman declined to comment, citing pending litigation. In the past, a company official said ITC responded immediately to the fire and had no lack of resources to put out the fire.

Asked how long it would take for investigators to get onto the grounds, ITC Senior Vice President Brent Weber said he hoped it would be days not weeks. “They have been on the site,” Weber said on Monday. “They’re staying out of the hot zone right now.”

Fumes and clean-up efforts continued to affect shipping for a third week. Twenty-two cargo vessels were able to transit the area near the ITC tank farm on Sunday, the Coast Guard said, between 40 percent and 50 percent of normal.

Another 64 were in a queue waiting to pass on Monday. In total, 118 ships were anchored outside the port, said U.S. Coast Guard Chief Petty Officer Derby Flory.

In addition to the state and county lawsuits, seven members of a Houston family have filed suit, claiming injuries from air pollution caused by the fire. Their lawsuit, which seeks $1 million in damages, alleges ITC failed to prevent the fire and did not adequately warn residents of the dangers once it began.

The seven were exposed to toluene, xylene, naphtha and benzene “causing them severe injuries and damages,” according to the lawsuit.

“The warnings were too little, too late,” said Benny Agosto Jr., who represents the family and whose firm is among at least four working to bring cases against the company.

(Reporting by Collin Eaton in Houston and Erwin Seba in Pasadena, Texas; editing by Gary McWilliams and Steve Orlofsky)