A number of Kenyan students sitting a chemistry practical exam have taken ill after being exposed to a poisonous chemical, the local Daily Nation newspaper reports.

One exam invigilator, a pregnant teacher, is also reported to have developed complications following the exposure. She was admitted to a hospital, the newspaper said.

The incidents have been reported in schools in Kisumu and Trans Nzoia counties in the country’s western region.

The Kenyan National Examinations Council (Knec) reportedly directed headteachers to buy and use xylene as an alternative for cyclohexane, which they were supposed to use, but which was unavailable.

Breathing xylene vapors in small amounts can cause headache, dizziness, drowsiness, and nausea, according to the Agency for Toxic Substances and Disease Registry. In some cases exposure to xylene can even lead to death.

During the practical exam, candidates were expected to heat the chemical and observe the sample without wearing protective gear.

It is not clear if officials at the education ministry were aware of the adverse health effects of the compound.

“We had to rush some of the students to hospital after the exam because they were complaining of chest pains, headaches and stomach discomfort. We gave milk to the rest,” a teacher is quoted as saying by the Daily Nation.

Meanwhile, teachers have accused the examinations council of negligence.

“Knec should not just be concerned about the integrity of the examination and overlook the health of the teachers who are manning the examination. Our lives matter,” a union official said according to the newspaper.

Knec has not yet commented.