Trapped Air Pressurized To Hundreds Of Pounds Per Square Inch Inside A Pumper Hose. Its Sudden Release Caused A Hose To Whip Violently, Throwing A Worker.
Inside the pipeline of a concrete pumper, air can get trapped and compress to hundreds
of pounds per square inch of pressure. The release of this air can cause the hose to suddenly whip.
Here, that cost one worker his life.
Two workers had just completed a porch using concrete supplied by a pumper truck. The truck’s pump was stopped and its boom was relocated to pour a walkway. One of the workers held the end-hose over the concrete forms.
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The concrete pump operator restarted the pump. He saw that the concrete wasn’t flowing. Realizing there must be a blockage, he immediately hit the emergency stop button. The blockage suddenly cleared. Concrete and air burst out, whipping the hose.
The worker’s heel caught on a piece of formwork. He then fell and struck his head on a 2 by 10. The worker did not survive his injuries. A hose whipping hazard is created if air gets into a pumper’s delivery system and is compressed against a blockage.
Air can get into a pipeline if the pump is stopped while the boom tip is in the down position. That’s what happened here. After the porch was poured, the pump was stopped with the boom tip down. Concrete was allowed to drain out of the last section of the boom. Concrete in the system then likely flowed back to the pumper’s hopper, sucking air in through the end-hose.
Now inside the pipeline there was a pocket of air. Restarting the pump pushed the concrete forward, compressing the air pocket like a spring against the blockage. Propelled by the pump and the compressed air, the blockage moved faster and faster through the pipeline. Seeing no flow, the operator pushed the emergency stop — but it was too late. The air and concrete blasted out, causing the hose to whip.
Hose whipping accidents can be prevented. Before starting a pour, warn workers of the hazard of hose whipping. Train workers to prevent blockages in pipelines and to recognize situations when air can get trapped behind a blockage. To minimize whipping, end-hoses should be no longer than allowed by the manufacturer.
A coupling should not be on the discharge end. The hose on this pumper was 20 feet long — 8 feet longer than allowed — and it had a coupling on the end. Hose whipping is a serious hazard. If you restart a pump after the boom tip has been down, ensure that workers stay clear of the end-hose until the concrete is flowing smoothly.