How to Write a Laboratory Procedure Using Flow Chart Method

By Linda Donahue
Flow charts help organize the steps for any procedure.

Because laboratory procedures tend to be an organized sequence of steps, with expected outcomes, the process can be represented with a flow chart. Using a flow chart makes it easy to follow the flow of the procedure, tracing it through the different outcomes, each to the proper ending. Because all laboratory procedures have different steps and different points in which multiple outcomes are possible, there isn't a single flow chart to represent all procedures. Constructing an appropriate flowchart, however, is an easy matter of putting together the correct symbols for each step involved. All you need to know is the proper symbol usage.

Draw a parallelogram to indicate a step in the procedure which requires input, such as material to be tested, or will produce output, such as a mixture.

Connect each box, which represents an aspect of the procedure, to the following box (or step) with a line. If you like, you can add arrows to the line to show the direction of flow, although typically, a flow chart flows naturally from the top down to the bottom. When you have lateral (or sideways) movement, however, you might wish to add arrows for clarity.

Use a basic rectangle for each of your straightforward processing steps in which there is only one outcome that will lead to the next step.

Connect to a diamond box when the step can produce more than one result. Perhaps this is a testing phase in your laboratory procedure in which the sample might test as positive or negative. (Or you might be testing for different ranges of values). For each outcome, draw a line from this diamond box to start a new branch of your flowchart. Label each branch with the outcome result, such as "positive" and "negative."

Use a round circle to represent the stop or end of a procedure step. Perhaps after a result comes up negative, there is no further testing. In this situation, the line would lead to an end circle.

Connect together parallelograms, rectangles, diamonds and circles in whatever order your procedure dictates until all paths either end at a circle or the path points back up to a previous step for situations where you must go back and repeat the procedure. Once all outcomes are covered, your laboratory procedure is completed.