ABCD is a pretty simple formula.

RD=LL+DD+HH+C isn’t so simple.

Yet for thousands of construction workers every day in Hawaii and elsewhere, both formulas represent basic — but not always so simple or followed — safety procedures that protect them from falls that could seriously injure or kill them.

On Wednesday, several hundred workers on three high-rise projects in Kakaako took an unprecedented timeout from work to witness simulated impacts from falling just 14 feet — a drop that can seriously mess up someone even if they have a safety line that catches them before they hit anything hard.

“You take an impact even without hitting the ground,” said Brad Foster, regional manager for 3M Capital Safety, a company that staged the 30-minute demonstration by dropping a steel weight to simulate differences between the force a 310-pound person absorbs if their fall was arrested by a taut line, a shock-absorbing line or an auto-decelerating line.

Taut safety lines were prohibited in the industry in the 1990s, Foster said, because the impact on a body from the line arresting a fall can be 2,500 to 3,500 pounds of force. “People used to get hurt bad,” he said. The legal limit now is 1,800 pounds of force, and safety lanyards are required for workers doing jobs 6 feet off the ground or higher.

Still, falls are the biggest killer in construction because of improper or absent equipment use. Foster said seeing a simulated fall makes a stronger impact on workers than classroom presentations, work-site briefings or safety cards.

3M Capital Safety also handed out cards printed with the easy-to-remember ABCD acronym for anchorage, body harness, connectors and descent rescue. Descent rescue refers to equipment used to lower an injured worker to the ground.

The other formula for safety, RD=LL+DD+HH+C, shows what workers need to know to calculate whether their fall-prevention equipment will stop them before they hit nearest obstruction. The required distance (RD) for a safety lanyard to be effective equals the lanyard length (LL) plus deceleration distance (DD) plus worker height (HH) plus clearance (C) from the ground or obstacle.

Getting this math right could be the difference between life and death. Hence the demonstration to stress the issue’s importance.

Milton Damas, an ironworker on the Waiea condominium project on Auahi Street makai of the Ward Village movie theaters, said seeing the demonstration was valuable, especially for some co-workers he knows who may be too stubborn to take the message to heart. “Hooking up safety-wise is very important being an ironworker up high,” he said.

Added fellowiron worker Tui Tuiloma: “It’s a must, or you going die.”

Rich Baldwin, national director of health, safety and environment for Denver-based PCL Construction, said the gathering Wednesday is the first instance he knows of where so many workers from unrelated general contractors convened for such a demonstration.

Participating firms were Nordic PCL, which is building Waiea, Albert C. Kobayashi Inc., which is building Anaha, and Layton Construction Co., which is building Ae‘o. All three projects are condo towers on adjacent blocks at Ward Village.

The construction firms organized the event as part of a national safety stand-down campaign held this week by the U.S. Department of Labor’s Occupational Safety and Health Administration to prevent construction falls.

OSHA says fatalities from falls are the leading cause of death for construction workers, accounting for 345 of 899 industry fatalities in 2014 nationally.

“Those deaths were preventable,” the agency said on its fall-prevention website, adding that fall-safety violations were among the top 10 citations issued by OSHA that year.