The National Transportation Security Board (NTSB) issued its first preliminary report Thursday on the Feb. 3 derailment of a train carrying hazardous chemicals in East Palestine, Ohio.

While the report seemingly faults an overheated bearing for the derailment, the NTSB investigation is ongoing, and a number of questions remain.

Here are five remaining questions about the train derailment:

1. Did the tank car design contribute?

In the preliminary report, the NTSB said it has decontaminated the train cars that contained hazardous material, which included vinyl chloride. Exposure to the substance, which is used for production of plastics, has been linked to higher rates of liver and lung cancer.

NTSB officials said they have removed and examined the top fittings from the cars that contained the substance, and those fittings will be sent to Texas for further testing.

2. What was the role of rail regulations or lack thereof?

Public safety advocates have frequently pointed to the Trump administration’s delay of a 2015 rule, vocally opposed by railroad companies, that would require the use of more modern electronically-controlled pneumatic brakes.

Although the Transportation Department has said the rule would not have prevented the East Palestine disaster, both Transportation Secretary Pete Buttigieg and President Biden have pointed the finger at the railroad lobby for deregulation and its potential role in the accident.

3. Are there still environmental hazards?

The NTSB noted in its report that it is not involved in “air monitoring, testing of water quality, environmental remediation, or evacuation orders” relating to the disaster. Much of this falls under the purview of the Environmental Protection Agency (EPA), which has taken over the response. EPA Administrator Michael Regan said last week that the agency will require Norfolk Southern, which operates the railroad, to assume financial responsibility for all cleanup efforts.

While the EPA and Ohio Gov. Mike DeWine (R) have said water in the area tested as safe to drink, they recommended drinking bottled water, and state officials have reported at least 3,500 fish have died in surrounding waterways.

4. Was the controlled burn the right move?

DeWine ordered an evacuation of the area days after the derailment. Shortly after and concerned about a potential explosion due to the presence of flammable compounds, first responders conducted a controlled burn. In its preliminary report, the NTSB listed “venting and burning of the vinyl chloride” as an ongoing subject of investigation. A number of lawsuits have been filed in the meantime alleging the controlled burn exacerbated hazards, including a complaint by local injury firm Morgan & Morgan claiming it has contributed to locals’ health problems.

5. How long will it take to determine the exact danger?

Many of the potential risks associated with environmental disasters — from cancer to developmental issues — can take months or years to become apparent and will require ongoing investigations by both the NTSB and the EPA.

Regan and Ohio Sen. Sherrod Brown (D) have urged residents to continue testing their homes’ air quality, and Brown has also said he is working to ensure Norfolk Southern does not manipulate residents into waiving their right to sue.

Another unknown is any possible risk to the surrounding areas, not just other parts of Ohio but the other side of the state line as well. Pennsylvania Gov. Josh Shapiro (D) told NPR this week that Norfolk Southern’s response has “given the middle finger to the good people of Pennsylvania and Ohio” and that testing of western Pennsylvania water is ongoing as well. “We’ve seen no concerning readings yet, but we’re going to continue to test for months and months and months, if not years,” he said.