An ergonomic analysis of the "Wagtail" window cleaning devices
Dr. Austin S. Adams Ergonomics Consultant
The University of New South Wales
The occupation of professional window cleaner is one which involves the day-long manual manipulation of several devices using a variety of awkward and often injurious postures and movements. The ergonomic problems associated with these manipulations have received little attention, perhaps because most window cleaners are self employed and hence do not generally have recourse to occupational health and ergonomic services.
The present analysis shows that the use of traditional window-cleaning tools involves the application of force with the upper arm in a variety of potentially-injurious postures. These postures are necessary because of the fixed relationship between the handle and the cleaning head of the traditional mop and squeegee tools.
A series of tools, the Wagtail squeegee, Wagtail mop and notably the Wagtail Combi (which combines mop and squeegee) have recently become available. These tools involve a novel and patented pivoting handle. An ergonomic analysis of window cleaning tasks using the Wagtail tools shows that their use can result in the virtual elimination of the major injurious postures of the upper arm involved in window cleaning. Their use on a pole can also reduce the amount of reaching and bending required during some window-cleaning tasks.
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', indicates that such trauma is common. The present report analyses these movements as carried out using traditional window-cleaning devices (which have a handle fixed at right angles to the cleaning head) and as carried out using a set of new window-cleaning devices, the Wagtail mop, squeegee and combi (a combined squeegee and mop that act together to clean a window). These new tools incorporate a novel and patented pivoting handle.
2. Window cleaning using traditional equipment
The traditional commercial window cleaner requires:
- a bucket of soapy water
A rectangular bucket into which the mop fits easily is generally used
- A mop or sponge
The mop, after removal from the water in the bucket, should not require undue "squeezing out" to prevent dripping as it is moved from bucket to window, but must still hold sufficient water to wet an entire window.
- 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 used to apply soapy water to the entire surface of 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 rubbing 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 back 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 "5" action. Typically, for a right handed operator the squeegee begins in the top left corner with the blade slightly past vertical and 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 than the bottom edge so that the squeegee turns through 180" as its direction is reversed. As shown in Figure 1, the movement from positions 1 to 4 involves a 180o 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.
3. An ergonomic analysis of the traditional window cleaning action
Figure 1. The movement of a traditional squeegee across the top of a window using the "5" motion. The handle is typically turned more than l80o each way every cycle.
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, for example hanging down from the shoulder. In this position the fingers and thumb are slightly curled, the palm is slightly cupped and the wrist very slightly cocked in relation to the forearm.
The possible deviations from this neutral posture are referred to as follows, assuming the forearm remains stationary and the wrist moves: Ulnar deviation is movement of the wrist sideways towards the little finger, radial deviation is movement of the wrist the opposite way, towards the thumb. If the forearm and wrist are held horizontally, palm down, dorsiflexion is a raising of the wrist and palmar flexion is a lowering of the wrist.
The two areas in which traditional window-cleaning operations involve potential stress on the wrist and forearm are:
1. In relation to radial and ulnar deviation. The maximum value of each of these movements is approximately 30" and it is recommended that a limit of about half of this should be observed'. More extreme deviations than this, particularly when force is involved, are associated with the pain and trauma of occupational overuse syndrome'(often referred to as "repetition strain injury").
2. 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 15º 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 almost fully supinated, which itself is a strain, and it is in almost the extreme position of dorsiflexion. Such strain can again be relieved by elbow movement-this time by adducting the elbow (towards, and even in front of, the body). There is therefore 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 lightweight 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.
4 The ergonomic implications of the Wagtail window-cleaning tools
Figure 2. The movement of a Wagtail squeegee across the top of a window using the "5" motion. The handle is typically turned no more than 90o each way every cycle, accompanied by a 90o rotation each way. With a slight alteration in technique, the same action is achievable using the Wagtail on a pole.
The new Wagtail tools incorporate several novel features, each of which has ergonomic implications for the execution of the window- cleaning task. Although there are three tools (a mop, a squeegee and a combination tool involving both of these in a single cleaning head), most of the references below will be directed towards the combination (" Combi") tool.
4.1 Rotating head
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 37o 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 20" to the glass-a 90o turning movement of the handle results in a 90o 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 Positions 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). 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 Breater 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 ttS" stroke can be implemented with lhe Wagtaii on considerably higher windows, and
they can be easily implemented using the Wagtail on a pole. ln practice, when a traditional squeegee is used with a pole the superior "S" stroke cannot be used at all.
4.2 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 then immediately squeegeed away 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 an 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 approximately 55o. 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. This means greater productivity with less effort. 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 lead to rapid evaporation of the applied water. The result is a partially dried window which increases the drag on the squeegee. To overcome this problem the cleaner tends to rush the operation resulting in increased exertion. With the Wagtail Combi, additional water is applied immediately in front of the squeegee blade by the attached mop, which ensures excellent lubrication of the squeegeeing action under all circumstances. This relieves the stress associated with (a) the need to push harder on a drying surface, and (b) the requirement that the entire operation be hurried.
4.3 Ability to rotate squeegee blade out of the way
Positioned on the cleaning head of the Wagtail Combi device, within reach of the thumb of either a left-handed or a right-handed operator, is a 17mm x 20mm plastic clip. lf 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.
4.4 The availability of three alternative tools
The Wagtail range of tools includes the Combi, a separate squeegee and a separate mop, each of which uses the pivoting head. Some window cleaners will choose to remain with separate squeegee and mop, and some window cleaners, even if they choose to use the Combi most of the time, will on occasion require separate squeegee and mop. The Wagtail range of tools accommodates all of these options and with all of them the advantages of the rotating head are retained.
Harmful movements can occur in window cleaning when the wrist is moved to extreme positions relative to the forearm. This is particularly so if these extreme movements occur with associated force. The Wagtail devices which have been examined allow the cleaning head to rotate to the required positions without requiring significant deviation of the wrist from its neutral position. Thus the Wagtail window-cleaning tools have the potential to remove most of the harmful movements from the window-cleaning operation, and, in addition, to improve productivity.
Using the Wagtail Combi ensures that the squeegee action is well lubricated with water, resulting in less effort and urgency when cleaning windows when the glass is hot. Reduced effort also results because the Wagtail makes it easy to maintain the optimal angle of the squeegee blade to the glass at all times. The result of the various design features of the Wagtail range of tools will undoubtedly serve to reduce