Implementing guidelines for lab work is done for different reasons. A primary goal of standard operating procedures is to ensure human safety and protect equipment as well as chemicals from being mishandled. Maintaining standards for quality assurance and quality control (QA/QC), so that valid data may be obtained is also a significant goal of standard procedures. Individual tests may have different and specific QA/QC procedures.
The Occupational Safety and Health Administration set standards to protect both workers and the public from potentially dangerous practices. There are specific requirements dealing with labs that use chemicals. As part of these requirements, as stated in OSHA standards 29CFR, there are specific action levels based on the concentration of exposure to a particular chemical that kick in other requirements such as medical monitoring.
Accuracy is a component of QA/QC monitoring, which basically means the ability of a test to give data that is correct. When considering accuracy it is useful to think of a bullseye. An arrow that hits the middle of the bullseye is completely accurate. Using known values of a substance to make sure they indeed exhibit these values when tested is a method to determine accuracy. This is mathematically calculated as tested value--known value/ known value x100= the percentage of error.
Tracking precision is also a necessary part of QA/QC and standard laboratory procedures. Precision is sometimes referred to as the "repeatability" of a test. Going back to the bullseye analogy, a grouping of arrows in any part of the target is displaying precision. If the grouping is outside of the center of the target, the arrows are still precise but are not accurate. Mathematically, precision can be represented by the relative percent difference of samples. This is done by taking sample one-sample two, dividing this by the mean of the two samples and multiplying by 100.
While each individual experiment generally has its own SOP which will guide the tester through the procedure, it is often necessary that the tester be qualified in order to follow the steps correctly. As pointed out by the California EPA Air Resources Board SOPs are often written so that an experienced technician can get the same results as would another experienced technician. Attention to detail and the ability to follow directions is a must for any lab technician.