Two young children are treated by paramedics after being affected by incapacitant spray as officers tried to arrest a man.
Officers used the Pava spray while attempting to arrest a man in Plymouth on Tuesday night.
Two children at the address were affected by the spray which causes severe pain to the eyes.
Devon and Cornwall Police said the children had been mildly affected and were now "fine".
A 22-year-old man is in custody in Plymouth following the arrest in the Keyham area of the city.
A police spokeswoman said: "The children were not directly involved, however when a substance like Pava is used in a small building such as a dwelling there is often some cross contamination.
"They were only mildly affected and are fine today."
Three officers were also injured during the arrest, including one female officer who suffered a serious blow to her head.
Pava is used by officers in potentially violent situations and is claimed to be significantly more potent than CS spray.
The spray is dispensed from a canister, is aimed at the eyes and causes severe pain by imitating the heat effect of natural chilli peppers.