US AUTHORITIES SAY an Iowa family’s attempt at a gender reveal party for a soon-to-be-born baby went horribly wrong when a homemade device that was meant to discharge coloured powder instead exploded like a pipe bomb, killing a 56-year-old relative.

The Marion County Sheriff’s office said Pamela Kreimeyer died instantly when debris struck her head Saturday before flying another 132 m and landing in a nearby field in rural Knoxville, about 35 km southeast of Des Moines.

Kreimeyer was 14 m from the device when it exploded.

Family members had been experimenting with explosives in the hopes of posting a colourful announcement on social media, authorities said.

They welded a metal cylinder to a stand and packed it with gunpowder that they thought would send the coloured baby powder aloft. But authorities say tape covering the top of the cylinder caused it to detonate like a pipe bomb.

Law enforcement officials expressed condolences to the family and warned about the dangers of using explosive materials.

“This family got together for what they thought was going to be a happy event with no intent for anyone to get hurt,” Sheriff Jason Sandholdt said in a statement.

What ended up happening was that Pamela Kreimeyer, a wife, mother and grandmother, was killed by a piece of metal where a metal stand gunpowder and coloured powder were involved. This is a reminder that anytime someone mixes these things there is a high potential for serious injury or death.

Using explosives to reveal a baby’s gender is rare, but a similar incident caused a major wildfire in Arizona in 2017 , when an off-duty border patrol agent accidentally set off a blaze that burned 189 sq-km of mostly Forest Service land.

The blaze forced about 200 people out of their homes and cost an estimated $8 million in damage and firefighting expenses. The agent, Dennis Dickey, fired a rifle at a homemade target that exploded, sending a blue substance into the air. The explosion started a grassfire that spread quickly.

Dickey pleaded guilty in September 2018 to a federal misdemeanour charge of starting a fire without a permit. He was sentenced the following month to five years of probation and was ordered to make an initial payment of $100,000 in restitution and monthly payments of $500.