In simple terms, WAI refers to how people think the work should be done whilst WAD is what people actually do to get the work done.
Work-as-imagined : Work-as-imagined is what engineers, planners, advisers, managers or anyone else involved in design believe the work should be done, under ideal circumstances. It’s the work-as-imagined picture that determines how a process is set up, how people are trained and which controls need to be put in place.
Work-as-imagined is an idealistic view of the formal task that doesn’t consider how task performance is adjusted to match the constantly changing conditions of work and of the world. Work-as-imagined describes what should happen under normal working conditions.
Work-as-done : Work-as-done is what people actually do to get the job done, taking into account the realities of the situation such as the equipment configuration, and ease of use of the procedure, and the time and resources they have.
Those who have to do the work may find they want to adjust the plans set out in the work-as-imagined in order to get their work done. If this happens without appropriate support, shortcuts may be taken or other habits adopted that can lead to errors.
However, if the difference between work-as-imagined and work-as-done is properly acknowledged and supported, then work can be adjusted safely and lead to reduced risk, increased reliability, and increased engagement.