Concurrency happens when two events occur at the same time. The meaning beyond this simple definition depends on the nature of the assessment: legal or technical. The SCL Delay and Disruption Protocol says that for two events to be considered concurrent, each opposing party must be liable for one of these events. This is because the SCL definition focuses on the contractual consequences of concurrency.

Unfortunately, casual readers often miss this detail, which leads to a misinterpretation of industry practices. Within the field of delay analysis expertise, concurrency should be discriminated according to the criticality of the concurrent events, disregarding liability. Alas, I have seen the devastating effects of such confusion in an arbitration case described below.


According to the Oxford Languages dictionary, concurrency is “the fact of two or more events or circumstances happening or existing at the same time”.

Within the construction industry, the Society of Construction Law Delay and Disruption Protocol is extensively quoted around the globe. The SCL Protocol says: “True concurrent delay is the occurrence of two or more delay events at the same time, one an Employer Risk Event, the other a Contractor Risk Event, and the effects of which are felt at the same time.”.

The fact that the SCL Protocol refers to the qualification of Employer Risk Events (ERE) and Contractor Risk Events (CRE) should immediately strike the attention of any experienced Delay Expert. This definition is for the Counsel, not the independent Expert. Indeed, since an event can only be qualified as ERE or CRE once liability has been established, and since liability is mainly outside the scope of Delay Experts, the Expert alone cannot run the concurrency test described by the SCL Protocol. Yet, I often see waves of criticism from peers when an Expert determines two events to be concurrently critical whilst it seems that both are an ERE or a CRE.

Employer Risk Events, Contractor Risk Events and Force Majeure

The SCL Protocol focuses on liability because this dictates the awards. An Employer Risk Event often grants the Contractor an extension of time and prolongation costs. On the other hand, a Contractor Risk Event grants nothing to the Contractor, which subsequently enables the Employer to claim liquidated damages over the late delivery of a scope of work.

True concurrency may allow mechanisms which often depend on contractual conditions and applicable law. The most famous mechanism is that of the Courts of England, which grants nothing to the parties because they are both liable: the Contractor cannot claim prolongation costs, and the Employer cannot claim liquidated damages. This is the odd “time but no money” paradigm. Another mechanism, often rooted in the Courts of Scotland, lies towards the apportionment of the liabilities. In my experience, this later mechanism is becoming less and less popular in International Arbitration.

Force majeure may also affect the ability of the parties to claim compensation. For example, FIDIC contracts and their derivatives often lean towards granting time but no money when the delay event relates to a natural disaster. My personal interpretation is that FIDIC aims to distinguish between unpredictable events strictly beyond parties’ control, such as severe adverse weather, and events indirectly caused by government bodies, such as strikes which may originate from new political policies.

When liability is at the heart of the dispute

On an infrastructure case I worked on many years ago, it had been determined that three concurrent delay events had impacted the progress to the critical earthworks: (i) the closing of a borrow pit by the local government for urban planning reasons, (ii) an exceptionally long heat wave, and (iii) national shortage of trucks due to strikes.

All three delay events were expected to qualify as force majeure events and therefore were sensed by the Expert to be Employer Risk Events. I say sense because only the Tribunal may characterize the liability of these events, which had dramatic consequences here. Hence, with all three events expected to fall under ERE, and in application to the SCL Protocol definition, it was established during the delay analysis that, as none of the three events were expected to be a CRE, there was no true concurrency. Consequently, only one of the three delay events was to be retained.

Since first the borrow pit was shut down, and only then the heat wave and the shortage of trucks took place, it was decided to present an expert report where the closing of the borrow pit was shown as the sole cause of delay to the earthworks.

Eventually, the Tribunal concluded that the closing of the borrow pit was not a force majeure and ruled for a Contractor Risk Event. Should the other two delay events had been characterized in the expert report as additional causes of delay, it is very likely that the Tribunal would have ruled in favour of true concurrency and an extension of time. Unfortunately, in the absence of other events mentioned by the Expert, the Contractor was granted nothing.

I hope this story illustrates how paramount it is to understand the distinction between the legal definition of concurrency, and that used in delay analysis and project management in general.

Delay Events Concurrently Critical

You may ask then, what would be a definition of concurrency from a delay analysis and project management perspective?

Establishing the basic concurrency of events, i.e., whether two events took place at the same time, is not really useful for a delay analysis. Instead, what is pertinent is establishing if they were both critical during the concurrency period. This is because delay events are only relevant if they delay the delivery of a scope of work, in which case they are said to be critical for that scope.

Hence, a definition could be that concurrent delay is the occurrence of two or more delay events along the critical path and at the same time. In practice, many colleagues and myself like to say that these delay events are concurrently critical. Such wording significantly reduces confusion.

In a subsequent article, we explore why experts often disagree on the critical path. If the critical path is disputed, it often means concurrent criticality and therefore concurrent delays are disputed too.

In this article:
Concurrency is one of the most argued topics in construction delay disputes. With this article, I intend to assist non-specialists in reaching an educated understanding of what concurrency is, and why concurrent delays are so often disputed.
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