The head of the National Transportation Safety Board said the agency "is working vigorously to understand what caused" the Feb. 3 train derailment in East Palestine, Ohio.
In a rare series of posts on Twitter on Thursday evening, NTSB Chair Jennifer Homendy issued "a message to the community" as well as "a plea to those spreading misinformation."
"To everyone affected: know that @NTSB is working vigorously to understand what caused this train derailment -- so it never happens again," Homendy tweeted. "You have my personal commitment that the NTSB will CONTINUE to share all information publicly as soon as possible following our analysis."
"Next: NTSB investigators will thoroughly examine the tank cars once decontaminated. As always, we'll issue urgent safety recommendations as needed," she continued. "Urgent safety recommendations may be issued at any time; meaning, we don't wait until the end of our investigation if immediate safety action is warranted."
She added: "Nothing…nothing is more important than accuracy at a moment like this, which is why the NTSB is deliberate in our approach to investigations. Credibility is ESSENTIAL to our lifesaving mission. The NTSB process WORKS.
MORE: Ohio train derailment: EPA administrator visits East Palestine, asks residents to 'trust the government'Homendy then tweeted: "That leads me to my last point: anyone speculating about what happened, didn’t happen, or should've happened is misleading a suffering community -- PLEASE STOP SPREADING MISINFORMATION."
The NTSB chair addressed speculation that a rule on electronically controlled pneumatic (ECP) breaks -- if implemented -- would have prevented the train derailment, which she said was "FALSE."
"The ECP braking rule would've applied ONLY to HIGH HAZARD FLAMMABLE TRAINS. The train that derailed in East Palestine was a MIXED FREIGHT TRAIN containing only 3 placarded Class 3 flammable liquids cars," she tweeted. "This means even if the rule had gone into effect, this train wouldn't have had ECP brakes."
Finally, Homendy urged members of the public to let her agency lead the investigation.
"Anything else is harmful -- and adding pain to a community that’s been through enough," she tweeted. "But…if this derailment has moved you to want to become a safety investigator, we'd love to have you at the NTSB."
Earlier this week, the NTSB shared an update on its ongoing probe into the incident, saying "investigators have identified and examined the rail car that initiated the derailment."
"Surveillance video from a residence showed what appears to be a wheel bearing in the final stage of overheat failure moments before the derailment," the NTSB said in the investigative update on Tuesday. "The wheelset from the suspected railcar has been collected as evidence for metallurgical examination. The suspected overheated wheel bearing has been collected and will be examined by engineers from the NTSB Materials Laboratory in Washington, D.C."
On the night of Feb. 3, about 50 cars of a freight train operated by Norfolk Southern Railway derailed in a fiery crash on the outskirts of East Palestine, a tiny village in northeastern Ohio, nestled near the state line with Pennsylvania. Ten of the derailed cars were transporting hazardous materials, five of which contained vinyl chloride, a highly volatile colorless gas produced for commercial uses. There were no injuries reported from the accident, officials said.
MORE: Experts struggle to gauge potential health impacts of chemical spill in Ohio train derailmentEfforts to contain a fire at the derailment site stalled the following night, as firefighters withdrew from the blaze due to concerns about air quality and explosions. About half of East Palestine's roughly 4,700 residents were warned to leave before officials decided on Feb. 6 to conduct a controlled release and burn of the toxic vinyl chloride from the five tanker cars, which were in danger of exploding. A large ball of fire and a plume of black smoke filled with contaminants could be seen billowing high into the sky from the smoldering derailment site as the controlled burn took place that afternoon, prompting concerns from residents about the potential effects.
A mandatory evacuation order for homes and businesses within a 1-mile radius of the derailment site was lifted on Feb. 8 after air and water samples taken the day before were deemed safe, officials said.
In the wake of the incident, FEMA will deploy a team on Saturday to help support ongoing operations in East Palestine, officials said.
"FEMA and the State of Ohio have been in constant contact regarding emergency operations in East Palestine, Ohio Gov. Mike DeWine and FEMA Regional Administrator Thomas Sivak said in a joint statement Friday. "U.S. EPA and Ohio EPA have been working together since day one."
The Incident Management Assistance Team will help with "incident coordination and ongoing assessments of potential long-term recovery needs," they said.
When asked about FEMA's absence, DeWine said during a press briefing earlier on Friday that he had been told they do not qualify for assistance -- and that he expected Norfolk Southern to continue to pay for the damage -- but that he had filed the necessary paperwork should FEMA's presence be necessary in the future.
Ohio Sen. Sherrod Brown tweeted Friday night that the FEMA team's advent "will be a huge help to the community."
It is unclear how long the FEMA team will remain in East Palestine.
The Department of Health and Human Services will be providing testing to the residents of East Palestine, DeWine said Friday's press briefing. A clinic will be established for residents to get assistance, evaluate symptoms and provide medical expertise, possibly as soon as Monday, he said. A team of medical personnel and toxicologists will conduct the public health testing, federal officials confirmed. More information can be found at ema.ohio.gov/eastpalestine.
The Environmental Protection Agency, in partnership with an independent contractor, continues to monitor the air in and around East Palestine. As of Friday, they have sampled air in 500 homes and throughout the community and have so far not detected contaminants either outside or inside the specific homes where they've been asked to monitor, DeWine told reporters.
The large chemical plume seen over the Ohio River has also completely dissipated, DeWine said.
DeWine's office announced on Wednesday that the latest tests conducted by the state's Environmental Protection Agency show five wells feeding into East Palestine's municipal water system are free from contaminants, and that the Ohio EPA is confident the municipal water is safe to drink.
Residents with private wells continue to be encouraged to drink from bottled water until their well water has been tested and cleared for consumption, the governor said Friday.
A section of Sulfur Run that is very near the crash site remains severely contaminated, officials said Friday. Teams are now working to pump in clean water to the section, which was dammed following the crash to contain any contamination. EPA officials have previously said that vinyl chloride or pre-product has been detected in the water, and that the contamination mostly consists of fire contaminant combustion materials.
MORE: Residents of Ohio town say they don't trust safety claims after train derailment, chemical spillDuring a visit to East Palestine on Thursday, EPA Administrator Michael Regan emphasized that residents should trust the testing if they're told it's safe to move back home. But he said individual families could make different decisions based on their health concerns and that families who haven't had their homes tested yet should stay away.
"If those homes have been tested and if those homes have been tested by the state and given a clean bill of health, yes, as a father, I trust the science," Regan told reporters. "I trust the methodology that the state is using. And as a parent, I would."
"I would encourage every family in this community to reach out to the state or EPA to get their home air quality tested and their water system," he added. "We have the resources to do it. We want to do it and want people to feel secure and safe in their own homes."
MORE: Waterways along Ohio River still contaminated following train derailment carrying hazardous materials: OfficialsRegan said that he understands why some residents are questioning the information they're being provided, while still asking them to "trust" the EPA and reach out to get their residence tested if they have any concerns.
"But for those who can't," he added, "I am asking that they trust the government. And that's hard. We know that there is a lack of trust, which is why the state and the federal government have pledged to be very transparent."
The EPA administrator has vowed to hold Norfolk Southern Railway accountable.
On Friday, the EPA said it has secured Norfolk Southern's commitment to cover clean-up costs, and that they are "exploring" a legally binding order to make that happen.
In an open letter released Thursday, Norfolk Southern Railway President and CEO Alan Shaw stated that the Atlanta-based rail operator has not abandoned East Palestine residents and is committing $1 million to a community support fund as a "down payment" on their contribution in rebuilding the village. He noted the work the company has already started, including cleaning up the derailment site and working to facilitate testing on the water, air and soil in East Palestine.
Earlier this week, Norfolk Southern Railway announced in a statement that it had helped 1,000 families as well as a number of businesses in East Palestine since the Feb. 3 train derailment. The company said it has also distributed $1.2 million to families to cover costs related to the evacuation.
"I hear you, we hear you," Shaw said in the open letter. "My simple answer is that we are here and will stay here for as long as it takes to ensure your safety and to help East Palestine recover and thrive."
White House spokeswoman Karine Jean-Pierre told reporters that the administration had a "a robust, multi-agency effort to support the people of East Palestine Ohio."
"We are committed to supporting the people of Palestine every step of the way and we are going to be on the ground helping them as long as it's needed. And also, we're going to hold Norfolk Southern accountable as well," she said Friday.
Jean-Pierre also noted that White House officials said earlier that the administration would be prepared to issue a legally binding order to get reimbursed up to three times the amount of the cleanup, if Norfolk Southern backed off their commitment to pay for the cleanup.
ABC News' Victoria Arancio, Peter Charalambous, Brandon Chase, Stephanie Ebbs, Alexandra Faul, Justin Gomez, Julia Jacobo, Ivan Pereira, Isabella Murray, Sasha Pezenik and Alex Presha contributed to this report.