Construction: Delay Versus Disruption Events
"Same same, but different..."
Even though Delay and Disruption both constitute the loss of time (and potentially un-recovered additional cost), there are some significant differences between these two concepts which are essential to understanding the nature of the events which cause them and how one may go about measuring their effects on the timing of a construction project.
What is the difference? In the simplest form; a delay is a total loss of time and disruption is only a proportionate loss, for example:
activity “A” should have started today, but only started the day after,
This would be a delay event, as opposed to:
activity “A” did start today as planned, however, it only progressed at half the rate due to an external influence.
Which would be a disruptive event.
This loss in productivity can be visualised as displayed within figure 1 below; here both the blue (undisrupted) and red (disrupted) lines represent identical portions of work starting on the same day, in this example 1 January (assume a seven day work-week).
The undisrupted activity was able to achieve its maximum expected output for the assigned resources on 5 January and was able to maintain this rate until 11 January before production slowed due to natural causes (demobilisation of labour, finishing works etc.).
Conversely, the disrupted period was not able to ramp up productivity as quickly as its undisrupted counterpart and was only able to achieve 70 percent of the production rate capable under normal circumstances. This lower rate of progress achieved ultimately resulted in this activity finishing three days later.
Here, the lower actual production versus that which is achievable, is the key element in separating a delay from a disruptive event.