That's the warning from WorkCover NSW following the launch of a safety campaign in Dubbo yesterday.

WorkCover district co-ordinator Mark Smith said falls through stair voids had been identified as a major safety issue.

To help get the message across, a safety video alert has been produced that builders and sub-contractors can download on computer, smart phone or tablet device.

"House construction is one of the state's most important industries, comprised of almost 9000 businesses that employ more than 44,000 workers, contributing $37.9 billion to the NSW economy," Mr Smith said.

"It's also one of the state's highest risk industries with more than 150 workers seriously injured or killed on the job in the last two years.

"This includes 69 workers compensation claims in the western and north-west NSW during that time."

Mr Smith said there were a number of things that could be done to prevent falls through stair voids.

"The safest approach is to plan ahead and have a fixed cover ready to install over any void," he said.

"The cover must be strong enough for people, materials and likely impacts.

"Where a fixed cover isn't possible, other safety measures include a working platform, temporary stairs or a physical barrier like a secure fence or edge protection.

"As part of the site management plan, it's also important to explain the site-specific void protection to everyone on-site and make sure they know what to do if changes are needed. This includes workers, subbies and other visitors to the site."

Dubbo firm BLD Constructions is building a house with a stair void and said the video would help communicate the risk of falls to everyone on the site.

"We have used a temporary hand rail to prevent falls through the stair void on this site," BLD Constructions part-owner, Tim Wright said.