Detective Chief Inspector Dick Pearson said: "These deaths are being treated as unexplained. The full circumstances of this tragic work-related incident are being investigated by the police with the assistance of the Health and Safety Executive."
More top news
Millions of voters headed to the polls to vote in today's local elections. Here is when the results are expected in.
Around 45 million registered voters in England, Wales, Scotland and Northern Ireland will vote in elections across the UK.
One year after the general election, this is Jeremy Corbyn's first big electoral test. Phil Hornby reports.