Ergonomic Analysis of Doors Connecting Malet Place Engineering Building to the Roberts Building

(This is unmarked coursework, part of my HCI course at UCLIC and is released with permission from Prof. Rachel Benedyk. Since this is not evaluated and hasn’t gone through any sort of peer review process, it will most certainly contain errors.)

This analysis uses static anthropometric data to find out inconsistencies of door measurements with the stature of the intended population and recommended positions of door artefacts such as push handles and see-through windows. It further uses dynamic anthropometry to find out if the restoring torque of the door is within recommended limits. The most common use case of a healthy adult is considered in detail as the target user group and the lack of wheelchair accessibility is also noted.

Door Dimensions

Figure 1: Approximate Measurement of doors

Static anthropometry does not reveal faults with the door width and height. According to data available, the width of the door at 93 cm (all measurements are described in detail in Figure 1) and height at 240 cm is adequately wide and high for the 95th percentile of the tallest man who at 180 cm tall (Pheasant 2003) serves as the limiting user. The recommendations for the door handle or push plate state that it should be 25-35 cm from the door edge and 100-150 cm above the floor (Chang & Drury 2007)—and we see that both the push plate and the door handle at 8 cm from the door has inadequate distance from the door edge. However, both have the requisite span since they are long vertical strips that have a length of 65 cm, making their total effective area close to 145 cm, well within the recommended space. Analysing the placement of the see-through door windows, a flaw is immediately obvious. In the case of a short woman as a limiting user (shorter than 140 cm), the window would be useless since it will not allow her to see an intended user on the other side. The major limitation of the static anthropometry method was that it did not consider the purpose of the door: i.e., it hypothesised a theoretical user and did not analyse the function of the door—to open and close and lead the user through.

We decided then to take a step back and use the doors ourselves and note down psychophysical observations. We also observed other people using the doors and noted down possible flaws in the door design. One problem was immediately obvious and unanimous: the doors were too heavy and couldn’t be pushed through easily. We noted an instance where a man walked in with a package, couldn’t use sufficient leverage to open the door with a single hand and instead kicked out with his leg to stabilise the door enough to move through. These observations made it evident that the heaviness of the door was a source of major ergonomic discomfort.

Taking into account Chang & Drury’s recommendations for restoring torque at 30 Nm, an analysis could be done after measuring the door width and the placement of the handle. However, the study was complicated by three factors: 1) the hinges on the door were badly in need of oiling, 2) the door had different resistances at different points in its axial opening and 3) the hinge was loose and at least a portion of the door was intersecting with the frame of the door causing added initial opening friction. Even ignoring these three factors, and calculating the torque of this door,

Moment = F r Sin a

Assuming a as 90 degrees, which means the user pushes the door at a right-angle,

Moment = F r

Since there was no way to measure the weight on the door, we assume a force ranging from 22 to 132 N as in Chang & Drury, moment at 22 N would then be: 22 N x 85 cm, which is 18.7 Nm. Assuming the upper limit of a 132 N force, moment would be 112.2 Nm.

We notice here that if the force on the door is beyond 35 N, we exceed the stated recommendations. The three subjective experiences noted above however, exceed any apparent weight of the door. The hinges of the door at the Malet Place end were so badly unmovable that they would not open beyond 70 degrees unless an exceedingly strong force was used. While any door is an interruption to the dynamic flow of walking of an individual, the successful doors try to stay out of the way by minimising resistance and being easy to open and close. The resistance of these doors makes even the strongest user take a cognitive break from his actions and use his will on the door to move through—this is especially evident when the user has his first experience since he does not expect the door mechanism to be so rusty.

Considering the operation of the door with normal users in mind, the biggest recommendation that can be made to ease the use of the door is to oil the hinges and position the door within the frame so that no part of the door impinges on the frame. The door could also be made lighter and conceivably transparent since it does not overlook into any sensitive areas. To ease wheelchair access, the door could be made powered. The placement of the door pads and the handle could be moved to be more conforming.

The doors would also probably require regular maintenance since they experience heavy traffic throughout the day. Because they connect two buildings with possibly separate and insulated heating systems, a heavier door might have been preferred, but the ergonomic cost add up after each use. Keeping in consideration cost requirements, an enclosed area between the two buildings could be constructed to serve the same purpose since the primary function of the door in this instance seems to be insulation.

While considering an evaluation of this nature, one thing that I thought could be done differently was to perform a contextual enquiry of people using the door—immediately after they went through the double doors. The users might be able to articulate what their material difficulty was, and provide clues to how to construct these doors better. The study could also have been better if it had more data to analyse: it would be relatively easy to set up video recording equipment and observe users interacting with the doors and analysing quantitative measures from the door as well, like the time it takes for a user to successfully complete the interaction. Perhaps grouped by gender, this can provide further insights.

(1047 words).

References:

Pheasant, Stephen (2003). Bodyspace. Anthropometry, Ergonomics and the Design of Work. Second Edition. p. 244.

Chang, Shih-Kai, Drury, Colin G. (2007) Task demands and human capabilities in door use. Journal of Applied Ergonomics Vol 38. pp. 325-355.