Piling rig concrete pumping hose whip fatality

Issued: 1/8/2025
Last Updated: 8/8/2025

Purpose

This safety alert highlights the risk of hose whip when compressed air is used to clean flexible concrete delivery hoses fitted to piling rigs with auger attachments. Additionally, it discusses the significant risks associated with the use of compressed air to clean any concrete delivery line and describes a number of risk control measures.

In 2024, a workplace fatality occurred when a worker was struck by a flexible hose fitted to a continuous flight auger (CFA) piling rig.

A CFA piling rig drills and fills a pile with concrete using a hollow-stem auger.

It is understood that the pipeline was being cleaned out at the end of the day using compressed air.

Preliminary investigations indicate one end of a flexible hose had been detached from a fixed steel line, the blockage cleared suddenly and the hose whipped violently under pressure, striking the worker.

IMPORTANT: These findings are not yet confirmed, and investigations are continuing into the exact cause.

Background

‘Hose whip’ normally describes the uncontrolled and rapid movement of the flexible rubber hose on the end of a concrete placing boom or other concrete delivery line. However, it can occur on any flexible concrete delivery hose when one end of a hose is detached while the line is pressurised.

The incident occurred on a piling rig fitted with a horizontal steel pipeline fixed to the body of the piling rig and a flexible rubber hose that was attached to one end of the steel line that ran vertically to the mast head. Another flexible hose ran from a trailer mounted concrete pump to the other end of the horizontal steel pipeline. The ends of the two flexible hoses were fitted with metal fittings so they could be attached to the steel pipeline with hose clamps and whip checks. Although this incident occurred on a piling rig, a similar incident could occur on any concrete delivery line where a flexible hose makes up part of the line and both ends are fitted with steel fittings (for example, on a typical line pump delivery hose).

Previous incidents have usually involved hose whip on the end delivery hose on a concrete pump where the hose has not been securely anchored (such as when tied to a structure or ground anchor system) or has been held by a worker. In these instances, serious injury can occur even though the end of the hose is not fitted with a steel fitting. However, steel fittings on the end of a hose can increase the severity of an injury to a person struck by the end of the hose.

Note: metal fittings must never be fitted to the end of the drop hose on a concrete placing boom or the end of a line hose (point of placement end).

A variety of methods are used for cleaning out concrete delivery lines as follows:

1. Reversing the pump: inserting a sponge in the end of the steel pipeline and reversing the pump, creating a vacuum in the system so that concrete is discharged into the hopper. In some instances, another sponge and a small quantity of water can be added to the end of the pipeline shortly after the process is started. In this method, the concrete that is sucked back into the hopper has to be discarded.

   Note: for hoses on mobile placing booms the concrete in the drop hose can be removed by hanging the hose vertically and letting the concrete fall out.

2. Water: towards the end of the concrete pour, filling the hopper with water so that water is pumped through the line to displace the concrete. Water cannot compress when pumped through the system so there is a reduced risk of stored energy being released from the system. In this process, most of the concrete can be used in the concrete pour as the volume of concrete in the line can be calculated. A partition, created by using sponges and/or 'Go-Devils’, is inserted into the line to separate water from concrete to prevent segregation. Just before water reaches the end of the line, the partition is discharged into a container for waste (the delivery hose and reducer have already been disconnected from the end of the placing boom). The contaminated water can then be stored on site and re-used with solids being progressively removed from the water.
3. Compressed air: pressurising the concrete delivery line with compressed air after attaching a blowout cap and placing a cylindrical or ball sponge at the start of the pipeline. Compressed air then forces the sponge through the pipe and pushes the concrete out the end of the line. In this method, the end hose must be anchored so that it cannot whip and the hose end directed into an enclosed bin or equivalent that can safely receive the pressurised concrete and the sponge.
   
   Note: while efficient, this method has the highest risk of the three methods and is therefore the least preferred option.

Of all the above methods, cleaning with compressed air is most frequently used on piling rigs.

If it is not reasonably practicable to use a safer way of cleaning a concrete delivery line and compressed air is to be used, it’s extremely important that safe work procedures and controls are implemented to minimise the risk to workers from hose whip and pressurised concrete striking workers.

Contributing factors

Most hose whip incidents occur in the following ways:

1. When clearing a concrete delivery line of concrete using compressed air, and a flexible hose has not been adequately secured.
2. When priming the concrete pump, re-starting the concrete pump after stoppages or when pumping down the concrete in the hopper at the end of a concrete pour.
3. When a blockage occurs and suddenly releases.
4. During the concrete pumping process when air is inadvertently sucked into a concrete delivery line because the concrete level is too low in the hopper. If hose whip occurs during pumping, the line hand, who is directing the rubber drop hose, will be at risk of injury. This risk can be avoided by ensuring adequate concrete levels are maintained in the hopper so that air is not sucked into the concrete delivery line.

In the first scenario, compressed air is used to purge concrete from the concrete delivery line when pumping is complete. Using compressed air to clear blockages is even more hazardous because of the increased air pressure being used. Some blockages cannot be cleared with compressed air because the blockage is too severe. An example of this is when a blockage occurs while using a typical 85-bar concrete pump. Applying compressed air will not be effective, as the pump’s pressure is significantly higher than that of a compressor.

Blockages can occur for a range of reasons including:

• debris discharged from the concrete delivery truck
• debris from agitator blades or build-up from dry cement patches
• gravity pushing concrete down a vertical run of the line resulting in head pressure being put on the concrete at the bottom of the vertical line
• long wait times between concrete being pumped, resulting in old concrete in the line
• a concrete mix design that has poor pumpability or bleeding characteristics ¹
• added resistance due to bends and pipe reducers
• delamination of the inner wall of twin wall pipes or wire braided hoses, such as long shards of steel in the pipeline or exposed wire inside hoses are more likely to cause blockages.

Hose whip can occur on any concrete delivery line arrangement where flexible hoses are not fully restrained (anchored) and the line is pressurised from the concrete pump or when using compressed air. Hose whip can be especially severe where a coupling on a flexible hose in the pipeline is removed while the line is still pressurised with air. As the length of unrestrained hose increases, so does exposure to the risk. For example, where there is an unrestrained flexible hose 20 metres in length, any worker within 20 metres of the fixed end is at risk of being struck by the hose.

A line could be pressurised in multiple locations due to factors such as air bypassing the sponge because the sponge is too small, damaged or is of an inappropriate material, or the concrete mix segregates into its different parts (i.e. especially in the case of vertical lines). A line could also be blocked in multiple locations.

There has been an increase in concrete pump incidents in Queensland where lines have failed, pipe clamps have been blown apart or hose whip has occurred. One of the reasons for this is that concrete mixes are becoming more difficult to pump and subcontractors are being engaged to pump concrete that has very poor pumpability. The resulting blockages and the associated incidents from attempting to clear these blockages, are becoming more common.

¹ Bleeding of concrete is a form of segregation where the mix water separates from the binder.

Action required

Concrete pumpability

Concrete pumps are used to build nearly every concrete structure where concrete is poured on site. Designers of concrete structures should therefore ensure the concrete being used in construction can be safely pumped by concrete pumping equipment typically available. This means that the concrete mix should be specified so that excessive concrete pumping pressure is not needed and the risk of blockages is minimised.

Concrete mix design is a complex field requiring extensive research and development. While concrete mixes are often selected based on their strength, durability, cost and “green” rating, they should also be designed for pumpability. The builder or principal contractor should check that a concrete mix is readily pumpable by consulting with the company pumping the concrete and the concrete supplier. This may mean having trial runs to pump concrete of the same specification to be used on site with the concrete pumping contractor’s involvement. Some preselected alternative mix designs that can have good pumpability should also be considered. Any pumping trial runs should be based on a specific mix design from a specific batching plant(s) that will provide concrete during the life of a project. It’s important that the engineer who designs the concrete mix is involved in this process.

The pumpability of concrete can also be adversely affected during heavy rain periods when the fines (fine particles of sand or crushed stone) are washed out of stockpiles at concrete batching plants.

In addition to being safer, designing a concrete mix that is easy to pump also makes good economic sense because the concrete can be pumped quicker and there will be less down time from attempting to clear blockages and replace damaged equipment.

Workplace Health and Safety Queensland’s Concrete pumping clamp failures safety alert provides further information regarding pre-pour planning and conducting a concrete pumpability trial.

Cleaning lines with air

If there’s a blockage suspected or detected in a concrete delivery line, compressed air should not be used to clear the blockage due to the risk of serious injury to workers in the area.

When using compressed air to clean concrete delivery lines that are not suspected of having a blockage, the following steps should be considered:

1. Ensure the blowout (washout) cap fitted to the line is fitted with a pressure gauge and an air discharge (dump) relief valve in addition to the air inlet valve. The air dump valve should be at least twice the diameter of the air inlet valve.
2. Be aware that an air compressor may not have adequate air pressure to completely purge concrete from the complete line. Particular caution is needed on CFA piling rigs where the work system selected may include purging of the concrete from the complete line including the vertical section of hose. Much greater air pressure will be required to move the concrete against gravity in the vertical section of hose. Although air pressure may be adequate to initially start the concrete moving, a blockage could still occur and stop concrete flow. If there’s risk of this occurring, shorter sections should be cleared of concrete, provided this can be done in a safe manner.
3. Ensure only experienced workers operate the valves on the blowout cap. Pressurising and depressurising the system needs to be done in a controlled and systematic manner at specific stages of the cleaning process. Sudden opening and closing of valves or doing this at the wrong time can cause violent explosions of concrete from hose ends. A high level of training for workers is required and this should include a trainee observing the operation first and then only carrying out the task under the direct supervision of an experienced worker. The employer should ensure it’s clear which workers are authorised to operate the blowout cap valves.
4. The pump operator should assess the workability of the concrete. If possible, reduce the friction of the waste concrete to be cleaned out of the line by increasing the slump before it’s discharged into the hopper. The operator must ensure that the concrete with added water is not poured into the element and that the water added doesn’t significantly alter the slump compared to the existing concrete in the line.
5. Only use cylindrical or ball sponges that are specifically designed for the diameter of the pipe being cleaned. Sponges should be clean and not have hard pieces of cement inside of them. Do not use rags or screwed up balls of paper, plastic or cardboard.
6. Recognise the signs of a blockage. During an air blowout, indicators of a blockage may include a sudden stoppage of concrete in the line or a noticeable increase in air pressure without any further concrete movement.
7. Always assume the line is under pressure until the sponge and concrete have been discharged from the end of the line and the line cannot be pressurised with air. Never open a pressurised line.
8. Be aware that it’s not only pressurised air in the flexible hose portion of the line that can cause hose whip. Pressurised air elsewhere in the line could pressurise concrete and cause hose whip.
9. In the event of a blockage, the lines should be cleared from the pump end working along the line towards the end until all lines are cleared. During this process there may be no alternative but to break the line and disconnect flexible hoses. However, it’s possible that even when the air is dumped, other sections of the line could still be pressurised with compressed air. A comprehensive process needs to be followed to determine the location of the blockage. Never break the line until all the compressed air has been dumped from the blowout cap. Ensure every hose end is secured from sudden movement before the pipe clamp is removed. A single restraint sling may not be effective at securing the hose end unless the hose end is secured firmly with a solid anchorage (limited to no slack in the sling). Where a restraint sling has to be disconnected while the line could still be pressurised, anchor the hose end in another way, such as by tying the hose end to the dipper arm of an excavator.
10. Before disconnecting the hose clamp, the hose end should be as far away from the worker’s face as practicable and pointing away from the worker. Suitable personal protective equipment including hard hat, face and eye protection should be worn by workers.
11. If a blockage is discovered in the line during the compressed air cleanout process, and the blockage cannot be removed safely, the section of pipe or hose with the blockage should be discarded but only after it can be safely removed.
12. Do not bash steel lines with hammers as this could cause the pipe to rupture and explode in a worker’s face (pipes can be brittle).
13. During the compressed air cleanout process, risk can be reduced by cleaning shorter sections at a time as there will be a smaller volume of compressed air and less explosive energy that could be released.

The Concrete pumping Code of Practice 2019 (PDF, 1.04 MB) has more information about preventing hose whip injuries, and actions to take when cleaning or clearing blocked pipelines including maintaining exclusion zones.