A federal court has blocked an attempt by the Trump administration to delay safety regulations for chemical plants – the latest in a string of recent legal setbacks for the administration in its attempts to reverse environmental standards.

An appeals court in Washington DC ruled on Friday that the Environmental Protection Agency could not delay the enforcement of a chemical safety rule drawn up by the Obama administration. The EPA’s attempt to impose a two-year delay on the rule was “arbitrary and capricious”, the court ruled, with judges criticizing the agency for making a “mockery” of the Clean Air Act.

The rule, which came in the wake of a 2013 chemical explosion that killed 15 people in West, near Dallas, set stricter standards for operators’ risk management plans.

Plant operators complained the rule was too burdensome, a view shared by the former EPA head Scott Pruitt, who announced the delay in June last year. A total of 11 states allied with environmental groups to successfully challenge this rollback.

“Again and again, the Trump EPA has tried to push through policies that jeopardize our health and fly in the face of the law – and again and again, we’ve taken them to court and won,” said Barbara Underwood, attorney general of New York, a state that has fought the EPA on the chemical rule and a host of other environmental issues.

“This is a victory first and foremost for the neighborhoods most susceptible to dangerous and toxic chemical releases,” said Andrew Rosenberg, director of the center for science and democracy at the Union of Concerned Scientists. “Families who live under the shadows of chemical facilities deserve safer practices to prevent future disasters.”

The loss for the Trump administration’s EPA is the third such setback for the agency in a week. On Thursday, a judge ruled that the administration had improperly attempted to delay clean water protections that Trump had called “horrible”.

This followed another defeat in which the EPA was ordered properly to address the dangers posed by chlorpyrifos, a toxic pesticide linked to brain damage in children.

EPA scientists had recommended a ban on the chemical, only to be overruled by Pruitt a few weeks after he met with Dow Chemical, the world’s largest manufacturer of chlorpyrifos. District judge Jed Rakoff said there “remains no justification for the EPA’s continued failure to respond to the pressing health concerns presented by chlorpyrifos”.

The state department has also fallen foul of the courts in its attempt to implement Trump’s agenda of sweeping away environmental rules and backing major fossil fuel projects. This week, a federal court ruled that the state department must conduct a more thorough environmental impact assessment in order to justify the construction of the controversial cross-border Canadian-US Keystone oil pipeline.