There are three ways you can estimate activity durations and the required resources.

1. You can consult with those in your organization that have estimating experience. Never be ashamed about revealing a lack of knowledge in an area. It is far worse to make a blunder and be found out. And by asking those who know, you will not only pay them a compliment, but also make their experience and knowledge yours at the same time.
2. You can use the project file of previous turnaround as a project template, if available. Unfortunately, such historical records are usually not available, or are incomplete, or are unreliable for a number of reasons. When using a project template you must be careful not to blindly copy previous mistakes (see Refining the Project Planning Process for more on this topic).
3. Or you can use project planning software, which has proven estimating formulas built-in (recommended over the use of a project template).

Most estimating know-how is empirical, which means it has been gained through first-hand experience. As you start estimating, you will gain experience and confidence in your ability. You will also become aware of whether the estimates are consistently on target, or whether you need to adjust them. This will allow you to gradually improve them to arrive at the most realistic estimates that will generate confidence and acceptance of your planning effort.

The correct way to estimate an activity is to define the steps involved, assign the necessary manpower and equipment, and then add a duration (in whole hours) sufficient for its execution.

For example: "UNHEAD EXCHANGER" will require two Boilermakers, one Equipment Operator, one Cherry Picker and an Impact Tool. Let’s analyze the component steps in order to estimate the duration for the activity:

We prefer to round upwards and convert into hours (for a total of 2 hours). Loosening and removing bolts could take less or much longer, depending on the condition of the bolts. Also, an extra hand (laborer) could be assigned to gather studs and nuts and place them in buckets for cleaning and to maintain workplace safety (to prevent workers from tripping over scattered bolts and sustaining injury). The crew can experience delays of all sorts: emergency evacuation of the area, tool and equipment failure, accidents, etc. This is the reason for rounding off all estimates on the high side - it tends to compensate for those unplanned events that can extend (delay) a job.

Another way to approach this - also rounding off durations to the high side - is to try to assign (add) at least 15% (fifteen percent) to every duration with manpower to cover personal, fatigue and delay factors. Personal factors cover items such as lunch, smoking and bathroom breaks. Fatigue factors cover the productivity loss experienced as workers become tired as the day progresses. Delay factors are all unplanned events such as equipment and tool failure/unavailability, accidents, etc.

But at no time should you include productivity adjustments in the estimates above and beyond the rounding up procedure outlined above. You should always estimate durations as realistically as possible: any adjustment for productivity loss should only be made against the total turnaround scope estimate. At that time you will be able to establish a realistic manhour budget.

The frequent temptation to "pad" the estimates is to ensure that there is sufficient "fat" in them to avoid overrunning the budget. It is better to be realistic, and include extra activities, wherever appropriate, to avoid overrunning the budget. These activities include:

• Worker sign up (hiring)
• Worker safety orientation
• Welder qualification testing
• Deliver blinds and tools to job site
• Repair / replace as necessary
• Clean up work area
• Return tools and blinds
• Haul off ___ to scrap yard

If the estimates are padded, and then someone adds a hefty contingency on top, you end up with so much waste that it will become obvious to the trained eye. This built-in inefficiency will result into a net cost overrun. The reason for this is the tendency to spend the available budget, or not to become alarmed unless it appears that the (padded) budget will be exceeded. So, if the resulting budget (padded with "fat" and contingency on top) is approved, in most cases hiring and manpower staffing will be higher than necessary. So, if you "pad" your estimates, you are assuring a certain amount of waste beyond what could be expected and/or tolerable. It’s easy to see why: having more workers than necessary results in having them standing around waiting on work.

In addition, you cannot saturate the area and expect good productivity. Scheduling more people than the number that can move about safely and efficiently only causes grid lock and slows everybody down. When that happens, morale is lowered, causing further deterioration of productivity. Also, rescheduling to alleviate such a grid lock results in extra movements (mobilization / demobilization) of personnel for the work involved.

One way to ensure sufficient elbow room for a smooth execution of the work is not to allow manpower density to exceed one worker per 150 square feet. This area is to be calculated adding up all surfaces (grade and platforms). This does not apply to work inside equipment, where the density is higher.