Trade unions, farmers and residents have taken to the streets in the northern French city of Rouen, demanding the government publish all data on the impact of a huge fire at a chemical factory amid fears for health and the environment.

The government has by criticised by residents and environmentalists since the fire broke out early last Thursday at a storage facility owned by Lubrizol, a manufacturer of industrial lubricants and fuel additives that is owned by the billionaire US investor Warren Buffett.

The blaze raged for nearly 24 hours last week, sending acrid black smoke billowing for miles around. The state has banned the harvesting of crops and sale of all produce of animal origin from a wide area in the region as a precaution while awaiting tests. Some farmers have been forced to dump tens of thousands of litres of milk in the past few days.

Facebook Twitter Pinterest The French prime minister, Edouard Philippe, walks past firefighters at the Lubrizol chemical factory in Rouen. Photograph: Lou Benoist/AFP/Getty Images

Many residents have said they did not feel reassured by local authorities’ statement this week that – despite the strong smell of hydrocarbons hanging over the city – people can “live and work absolutely normally”.

State authorities said tests showed no harmful toxins in the air or city water. Schools reopened this week after closing for a few days for intensive cleaning to remove black soot, but some staff in secondary schools refused to go back to work, saying children were suffering from headaches.

Corinne Lepage, a former environment minister, lawyer and environmentalist, lodged a legal case this week urgently demanding all information on the fire, saying it seemed the state was only revealing partial details.

Facebook Twitter Pinterest A farmer shows her hand covered with black dust near Rouen on Monday. Photograph: Lou Benoist/AFP/Getty Images

For days, residents have demanded a full list of chemical products that burned in the fire. The French prime minister, Edouard Philippe, on Wednesday finally told parliament a list would be made public.

Earlier, Philippe had told residents in Rouen that the lingering smell was “a nuisance” but not dangerous. He promised transparency by the state.

After the fire, residents were told not to eat fruit or vegetables from gardens without washing them thoroughly, and not to touch the soot or other particles on the ground. Fire officers who fought the blaze were being tested to determine the impact to their health.

Facebook Twitter Pinterest Firefighters at the scene of the Lubrizol blaze on 26 September. Photograph: AFP/Getty Images

The day after the fire, France’s health minister said she could not guarantee there was no risk to the public after the massive fire spewed smoke and soot.

“The city is clearly polluted,” Agnès Buzyn said after visiting the scene, adding: “I cannot guarantee that there is no danger. There are of course traces of hydrocarbons.”

Fears and mistrust over the official government line about the Rouen fire follows concerns about possible health risks from the Notre Dame cathedral fire in Paris. An environmental group has filed a lawsuit in the capital saying swift action was not taken to contain potential lead poisoning from the cathedral blaze.