Quick hitch devices on excavators
Summary
This guidance describes what a quick hitch is, discusses common failure modes, in particular with semi-automatic hitches, and directs inspectors to take action in response to certain site scenarios.
Introduction
The purpose of this guidance is to address key issues that inspectors should wish to consider during relevant inspections and gives guidance on instances where enforcement may be appropriate.
A quick hitch (QH) on an excavator is a latching device that enables attachments to be connected to the dipper arm of the plant and interchanged quickly. An excavator operator may change the bucket on his excavator up to 30 times a day in order to maximise the machine productivity.
A significant number of all accidents investigated on excavators are attributed to the bucket detaching from a QH and injuring a ground worker, most of which are fatal and major injuries. However, there may be many more dangerous occurrences that occur that might not be reported when a bucket detaches unintentionally from the hitch, but without injury because no one is underneath at the time.
Action
Inspectors should ask the following questions when assessing the safe management of QH use:
- Ask site supervision if the QHs on the excavators under their control require a manual safety pin (they should know)
- Is the risk of bucket detachment covered by their risk assessment?
- In addition to evidence of training in operating the excavator, have excavator operators been trained in the use of their QHs, and, where appropriate, in the use of the excavator as a crane? (NB: The CPCS excavator operator course has covered QH since January 2008. CPCS cards dated before this will not include testing/training on a QH and cannot be relied upon to demonstrate competence).
- Is there a checklist in the cab of daily and weekly inspection and maintenance carried out on the excavator, and does this checklist include a check of the QH and lubrication as appropriate? Is there a record of the inspection and maintenance actually carried out?
- What are their management systems for checking whether manual safety pins are always in place?
- Whether the safety pins are inserted where appropriate. (If the pin is missing, try looking behind the driver's seat!)
- Can the operator explain the type of QH system they have (do they know whether it needs a safety pin or not?) and is a manual or instruction card available in the cab?
- Does the operator know how to visually check that the QH is locked?
- Does the operator know that, for all types of QH, they should test the security of the bucket after changing it? [Some manufacturers advise "shake, rattle and roll", others suggest placing the bucket flat on the ground then trying to uncrowd the bucket so that the bucket tries to disengage from the QH].
If inspectors suspect that the QH is malfunctioning or has parts missing evidenced by:
- The latch on hydraulic types moving in a jerky action;
- Any obvious missing or broken parts; or
- Hydraulic pipes close to the hitch badly damaged.
Then inspectors should request involvement of their local SG mechanical specialist.
Advice to duty holders on good practice can be found in HSE's safety alert to the industry on quick hitches of 17 December 2007.
Inspectors should establish whether the hitch is permanently attached to the excavator and ensure that the hitch is part of the thorough examination as part of the machine or as an accessory depending on the response given.
See Appendix 1 for recommended enforcement action and Appendix 2 for photographs of what to expect.
Background
Manufacturers
Typically, the QHs are not made by the excavator manufacturer, although some QHs are 'badged' with the excavator manufacturer's name and are supplied by them. There are known to be 20 or more manufacturers on the market, most of whom have several different designs of QH.
A standard bucket is secured to the dipper arm with two pins. QHs may pick up a standard bucket using the original pins, or the QH may have a dedicated attachment system that only fits buckets with matching engagement lugs. The advantage of dedicated systems is that the original radius of bucket movement can be maintained by compensating for the thickness of the QH, thus keeping the same break out force as the manufacturer intended. The disadvantage is less flexibility because only dedicated buckets can be used. In addition, a significant investment in dedicated buckets and attachments is required. For this reason most systems are 'pin' type rather than dedicated type.
Quick hitch systems
The QH systems on the market can be manual or non-manual. Non-manual systems are known as semi-automatic and automatic:
- A manual system requires the operator to change the bucket by, for example, winding a screw thread to open and close a latch, or using a bar to open a spring actuated latch. Although faster than the conventional method of bucket change, this method is relatively slow and cannot be done from the excavator cab.
- Non-manual systems use a hydraulic ram to move the latch to retain the bucket.
- Semi-automatic systems (Appendix 2 photo 1) require the operator to leave his cab after he has operated the QH latch to insert a retaining pin in the hitch as additional security. This pin usually works by locking the latch in its closed position; this is often referred to as the "safety bar" and it is not a load bearing part of the hitch. The safety pin cannot be inserted unless the latch is in its fully closed position.
- Automatic systems (Appendix 2 photo 2) can be operated entirely from the cab and usually have an independent locking system which functions automatically and which does not rely on hydraulic pressure to hold the latch in its closed position. Automatic systems should have a method where the operator can verify that the hitch is locked from the cab – for example, locking pins may protrude from the side of the hitch when the latch is in its unlocked state. Large attachments such as rammers may prevent the locked condition being verified from the cab, in which case, the driver needs to get out of his cab to check the locked condition.
QH systems have become increasingly common and now many large excavators and some mini-excavators are fitted with QHs. QHs need to be maintained and may well be replaced during the life of an excavator. If they are replaced, then it is important that the controls are compatible with the new hitch, or are replaced at the same time.
Although incidents have occurred with automatic QHs, accident statistics suggest that the majority of incidents occur on semi-automatic systems where a manual safety pin should be inserted, but where the operator failed to do so. See Appendix 3 for detailed reasons why this may be the case.
Thorough examinations
If the QH is used for lifting (many QH's have a lifting eye for this purpose), the weight of the QH has to be deducted from the SWL of the excavator. QHs fitted with lifting points/attachments are subject to the requirements of Lifting Operations and Lifting Equipment Regulations (LOLER) 1998. See Appendix 4 for details of QHs and thorough examinations.
Organisation
No special visits or other organisational requirements are involved.
Further References
- HSE webpage – Industry guidance on quick hitches (safety alert 17 December 2007)
- HSE webpage – Industry takes action on semi-automatic quick hitches from 1 October 2008
- HSE webpage – Frequently Asked Questions (FAQs) on quick hitches
Contacts
Construction Sector Safety Unit.
Appendix 1: Recommended enforcement action
| Issue | Action |
|---|---|
No SSW: (Management are not aware whether safety pins are required, or do not carry out routine checks) |
Consider IN (MHSW 5(1)) |
No SSW: Ground workers are required to work below excavator buckets fitted with QHs |
PN and possible prosecution |
No pin fitted when it should be |
Consider PN (PUWER 5(1)). If more than one instance on the same site consider prosecution |
Evidence that operator does not know how to use hitch |
PN (PUWER 7(2)) on hitch (work can continue if hitch is removed and bucket replaced directly on the dipper) |
Evidence of poor maintenance |
IN or PN (PUWER 5(1)) if hitch appears likely to cause bucket detachment. Involve SG if necessary |
No risk assessment covering bucket detachment |
Letter or IN (MHSW 3(1) or 3(2)) |
Appendix 2: Photographs – what to expect
Photo 1: Semi-automatic type of QH (Safety pin about to be inserted)
Photo 2: Automatic type (Closed position)
Appendix 3: Reasons why the majority of incidents occur on semi-automatic systems
This may be the case because:
- The bucket is changed frequently and the operator may on occasion fail to fit the safety pin in order to reduce the changeover time.
- The excavator is working in poor conditions (eg mud, heavy rain) and the operator is reluctant to leave the cab to fit the safety pin.
- The operator may not have been adequately trained in the use of QHs, and is unaware of the need to insert the safety pin. (The excavator may be hired, and the operator may be familiar with the excavator, but not with the particular type of QH).
- A pin may not be available, having been lost or misplaced.
- Some hitches have two holes for the safety pin (in order to pick up different bucket sizes) and the pin may have been inserted into the incorrect hole by mistake.
There is a management issue in ensuring that the safety pin on semi-automatic hitches is always fitted. In some cases, supervisors may not be aware of whether a pin is required or not, or how to check whether it is in the correct position.
In addition to precautions relating to the way the QH is operated, the basic precaution of ensuring ground workers are not required to work close to, or under the bucket (for example, within an excavation) should be strictly maintained.
Appendix 4: Quick hitches and thorough examinations
If the QH is permanently attached to the excavator, then it can be treated as though it is part of the machine and should be thoroughly examined at least every twelve months, unless either there is an examination scheme which determines otherwise, or a competent person has set a different period, for example, due to its condition, or to particularly harsh operation (eg use with a hammer).
If the QH is not permanently attached to the excavator, then it should be treated as a lifting accessory and have a thorough examination every six months, or in accordance with an examination scheme.
Since the implementation of the Supply of Machinery Regulations 2008, there has been discussion between HSE, manufacturers, suppliers and user trade associations regarding the reclassification of couplers. This is an ongoing debate and further details will be provided, once a definitive legal position has been given via Europe. In the interim however, HSE categorises new QHs in accordance with the Supply of Machinery Regulations 2008 as interchangeable equipment.
This means each hitch should be CE marked and provided with a Declaration of Conformity (D of C), and this declaration fulfils the requirement of a thorough examination for the 12 months following the date on the D of C. After this date, thorough examination of the quick hitch is required if suitable for use in lifting operations. For QHs supplied by the excavator manufacturer as part of the original equipment, the D of C for the excavator is sufficient.