Given that the most current standard deals with only a limited set of conditions compared to the actual working environment of a fume hood, it is frequently a challenge for a designer to know exactly what to do in terms of fume hood control. One method of dealing with the often conflicting advice from experts in the field and from suppliers' marketing departments is to use a form of value engineering called functional analysis, which involves the following steps:

• identifying the objective or what is to be optimized - in this case hood containment
• identifying all the main functions - the factors affecting hood containment
• identifying the relative influence of each factor on the objective and on other factors
• assigning relative weights to each of the factors based on the best knowledge available
• ranking the factors in order of importance according to the relative weights
• basing the design specification on the functional analysis

As an example, in the case of fume hood containment, factors affecting performance could be listed in random order as follows:

• hood design
• hood materials
• face velocity profile
• user work practices
• installation conditions

Additional factors, classified as dynamic challenges, could be as follows:

• sash movement
• air diffusion patterns
• pedestrian traffic in front of the hood
• room static pressure changes
• duct static pressure challenges
• transient face velocity fluctuations
• challenges caused by an experiment

In the value engineering exercise, these factors are usually shown as a number of smaller circles surrounding a larger circle, which represents the objective - in this case containment. Following is a list of typical factors that apply to containment:

• hood design
• hood material
• sash type
• face velocity profile
• work practices
• installation
• experiments
• face velocity transients
• pressure changes
• lab traffic
• air diffusion
• sash movements