Independent Ergonomic Report
This is the ergonomic report of Wagtail tools conducted independently by the leading ergonomist, Dr Austin Adams of the University of New South Wales.
An Ergonomic Analysis of the ” Wagtail ” Window Cleaning Device
Dr. Austin S. Adams
The University of New South Wales
The occupation of window cleaner is one which involves the day-long manual manipulation of a device using a variety of awkward and often injurious postures and movements. Although little has been recorded in the literature concerning occupational overuse syndrome in window cleaners, anecdotal evidence from window cleaners, as well as the occasional article in trade publications (Reference 1) indicates that such trauma is common. The present report analyses these movements as carried out using traditional window-cleaning equipment and as carried out using a new window-cleaning device, the Wagtail , which incorporates two novel features- a pivoting handle and the combination of mop and squeegee. The effect of these innovations is to reduce significantly window-cleaning movements and forces which have the potential to cause occupational overuse syndrome.
WINDOW CLEANING USING TRADITIONAL EQUIPMENT
The traditional commercial cleaner requires:
• A bucket of soapy water
A rectangular bucket into which the mop fits easily is most convenient
• A mop or sponge
The mop must hold sufficient water to wet an entire window, but should not drip water as the mop is moved from bucket to window. It should not require undue “squeezing out” after dipping into the bucket of water.
• A squeegee
The squeegee has a rubber blade which must have a sharp edge to enable efficient removal of water without undue pressure. As the blade wears so additional pressure is required.
The cleaning operation is as follows:
1.The mop is dipped in the water and the soapy water is applied to the window. Where shop windows are cleaned regularly the soil present is usually only a thin layer of dust, together with minor streaks and oily finger marks, all of which can be removed without any deliberate scrubbing action. The passing of the mop over the surface of the window with sufficient pressure to apply an even layer of water is all that is normally required.
2 .The mop is then exchanged for the squeegee. A common action would be for the operator to put the mop into the bucket of water and take the squeegee from a belt holder where it would be kept when not in use.
3. The window is dried with the squeegee. An experienced operator uses an “S” action. Typically, for a right-handed operator the squeegee begins in the top left corner with the blade slightly past vertical, with the handle pointing slightly upwards. It is moved horizontally across the width of the window, remaining approximately vertical until it is one squeegee width from the right-hand edge. At this point the top edge of the squeegee is moved faster that the bottom edge so that the squeegee turns through 180â as its direction is reversed. As shown in Figure 1, the movement from Position 1 to 4 involves a 180â turn of the squeegee handle. At this point the squeegee is moving horizontally across the window in the other direction, but one squeegee width lower down the window. The complete action is illustrated in Figure 1.
AN ERGONOMIC ANALYSIS OF THE TRADITIONAL WINDOW CLEANING ACTION
In the following analysis, the “neutral” posture of the hand in relation to the forearm will be referred to. In this position the forearm and hand adopt the relative position they are in when completely relaxed, hanging down from the shoulder. In this position the fingers and thumb are slightly curled, the palm is slightly cupped and the wrist slightly cocked. In particular, there is neither ulnar (movement towards the little finger) nor radial (towards the thumb) deviation of the wrist in relation to the forearm, nor is there dorsiflexion (towards the back of the hand) nor palmar flexion (towards the palm) of the wrist.
The two areas in which traditional window-cleaning operations involve potential stress in the wrist and forearm are:
• In relation to radial and ulnar deviation The maximum value of each of these movements is approximately 30â and it is recommended that a limit of about half of this should be observed (Reference 2). More extreme deviations than this, particularly when force is involved, are associated with the pain and trauma of occupational overuse syndrome (Reference 3)(often referred to as “repetition strain injury”).
• In relation to the use of the pinch grip rather than the power grip There are two types of grasp which can be used by the hand. The power or palmar grasp, such as is used to grasp a hammer, involves the whole hand and is controlled largely by relatively strong muscles within the forearm. The other grip, the pinch grip, such as is used to grasp small objects such as a needle or pencil, enables much finer manipulation but it involves much weaker muscles within the hand itself. The pinch grip, when used constantly, and with force, is associated with the pain and trauma of occupational overuse syndrome.
The traditional window-cleaning method described above involves the use of a squeegee in which the handle is fixed in relation to the blade. The following analysis assumes that the handle of the squeegee is held in a palmar grip.
The movement begins, as shown in Figure 1 Position 1, with the wrist positioned with approximately 15â radial deviation. This radial deviation is felt as a strain which can be minimised by raising the elbow. Such raising of the elbow can bring the forearm into the neutral position, but at the expense of the shoulder tension required to raise the elbow. Where a shop-front window which may be 2m above the ground is involved (ie not so high that a pole is required) the action required to raise the elbow so as to reduce the radial deviation of the wrist in Position 1 is such that the shoulder is almost fully flexed. Thus the basic starting position has the potential to involve either wrist or shoulder strain.
By the time Position 2 (Figure 1) is reached, the forearm is in the neutral position and the elbow is naturally lowered.
By Position 4 the wrist is supinated and is in almost the extreme positions of both dorsiflexion and ulnar deviation. Such strain can again be relieved by elbow movement – this time by adducting the elbow (towards, and even in front of, the body). Thus there is, again, strain in either wrist or shoulder.
An alternative grip is to use a pinch grip, holding the squeegee lightly in the fingers. Such a grip involves practice and discipline. If a very light grip can be maintained – requiring a light-weight squeegee and a sharp rubber squeegee blade – stresses on shoulder and wrist can be reduced because the wrist can be maintained for much of the movement in a position which is closer to the neutral position. However, any tendency to use a pinch grip with force will involve strain within the intrinsic muscles of the hand, possibly leading to occupational overuse symptoms.
THE WAGTAIL WINDOW-CLEANING DEVICE AND ITS ERGONOMIC IMPLICATIONS
An alternative device to the traditional fixed-handle squeegee is a new device which the manufacturer calls the Wagtail cleaning tool. This device, illustrated in the accompanying photographs, incorporates several novel features, each of which has ergonomic implications for the execution of the window-cleaning task:
The 400mm wide cleaning head is free to rotate in relation to the handle of the device. Specifically, the axis of the handle lies at 37â to the plane in which the cleaning head rotates. This means that, when the cleaning head is placed on the window with the rubber squeegee blade at the correct angle to the window – ie with the handle at 20â to the glass – a 90â turning movement of the handle results in a 90â rotation of the cleaning head on the window.
The main ergonomic implication of the rotating head is illustrated in Figure 2. At the start of the cleaning movement (Position 1) the wrist is almost exactly in the neutral position. As the cleaning head is moved across the window through Position 2 to Position 3, a slight rotation of the handle, achieved by a lowering of the elbow and a supination of the forearm, rotates the cleaning head. At Position 4, with the forearm supinated, the wrist is still largely in the same neutral position it occupied in Position 1 (where the forearm was pronated).
Figure 2. The movement of a Wagtail device across the top of a window using the “S” motion. The handle is typically turned no more than 90â each way every cycle, accompanied by a 90â rotation each way. With a slight alteration in technique, the same action is achievable using the Wagtail device on a pole.
Thus a natural rotation of the forearm each way produces the required rotation of the cleaning head without requiring undue deviation of the wrist from its neutral position. The basic window-cleaning movements can thus be achieved with the Wagtail device by using body movements which are almost totally benign from the point of view of their likely production of occupational overuse symptoms.
A further ergonomic implication of the rotating head is that, with the wrist held at a given height, the reach of the device, both up and down, is increased by approximately 120mm. A better way of looking at this from the ergonomic point of view is that, for a given window, the wrist needs to be raised less to clean the top and lowered less to clean the bottom.
The facility for reaching higher that is provided by the rotating head leads to an even greater advantage when a pole is used with the Wagtail. As illustrated in the accompanying photographs, the Wagtail cleaning head can be maintained at the required angles for the preferred “S” squeegee action against a much higher window than can a traditional squeegee.
With a traditional squeegee a high window requiring a pole can only be squeegeed using single descending strokes successively across the window’s width, with the squeegee horizontal at all times. These strokes require a relatively deep bend on each stroke and, because the squeegee is offered to the window at a varying angle as it descends down the window, greater forces must be applied to the squeegee than are required if the correct angle of rubber blade to window can be maintained, as happens during the “S” stroke illustrated in Figures 1 and 2.
Thus the smoother, freer movements requiring less bending that apply during the “S” stroke can be implemented with the Wagtail on considerably higher windows, and they can be easily implemented using the Wagtail on a pole. In practise, when a traditional squeegee is used with a pole the superior “S” stroke cannot be used at all.
MOP AND SQUEEGEE COMBINED
A mop is incorporated in the cleaning head and is fixed immediately proximal to the rubber squeegee blade. Thus, in use, water is applied and is immediately squeegeed off with a single pass of the cleaning head over the window. The mop is a piece of carpet-like material fixed to a flat section 375mm long (ie slightly shorter than the rubber blade) and 35mm wide, cut away at a 45â angle at the ends to allow the squeegee to reach into corners easily. The mop is fixed to a flat plane positioned on the cleaning head so that when the mop surface is flat on the window the squeegee blade, resting in front of the mop, is automatically offered to the window at the correct angle of 55â. The depth of the mop surface is such that it is easy to maintain the mop surface flat on the window and therefore easy to maintain the squeegee at the correct angle with a minimum of wrist tension.
The combining of the mop and squeegee can remove the requirement to apply water in a separate action – the single pass of the Wagtail device over the window surface applies water and then immediately squeegees it away, meaning either greater productivity or, more appropriate to the present analysis, less effort for the same productivity. If conditions are such that a separate mopping action is required then that mopping action can be accomplished with much less precision, as a second mopping action will be accomplished by the Wagtail in the same pass as the eventual squeegeeing.
On hot days, sun striking a window can make the window very hot. There is then a tendency for window cleaners to rush the window-cleaning operation because applied water can easily dry before the squeegeeing operation is completed, thus leading to increased drag on the squeegee with the associated requirement to press harder on the tool.
With the Wagtail , additional water is applied by the mop incorporated into the cleaning head which ensures excellent lubrication of the squeegeeing action under all circumstances, thus relieving the stress associated with (a) the need to push harder on a drying surface, and (b) the requirement that the entire operation be hurried.
Ability to rotate squeegee blade out of the way
Positioned on the cleaning head of the Wagtail device, within reach of the thumb of either a left-handed or a right-handed operator, is a 17mm x 20mm plastic clip. If either of these is very lightly depressed the squeegee blade can be rotated out of the way, leaving the mop alone. This feature permits the single Wagtail tool to provide a separate wetting down or mopping action should that be required. Appropriate circumstances might be where the window is unusually dirty, or if the window cleaner wishes to leave the cleaning water on the window for a short time to allow it to soak into and loosen any dirt.
Where a separate mopping action is required the Wagtail tool allows it to be accomplished without the bending and associated movements required to change tools.
The Wagtail window-cleaning device has the potential to remove most of the harmful movements from the window-cleaning operation and in addition, to improve productivity. Harmful movements can occur in window cleaning when the wrist is moved to extreme positions relative to the forearm, and particularly if this occurs with associated force.
The Wagtail device allows the cleaning head to rotate to the required positions without significant deviation of the wrist from its neutral position. In addition, by ensuring that the squeegeeing action is well lubricated with cleaning water, and by ensuring that the angle of the squeegee to the window is maintained without undue effort, two other possible causes of the requirement that additional forces be applied to the work are removed, further reducing potential sources of occupational overuse symptoms in window cleaners.