Moisture Vapor Transmission Rate (MVTR)

Definition - What does Moisture Vapor Transmission Rate (MVTR) mean?

A moisture vapor transmission rate (MVTR), also referred to as a water vapor transmission rate, is the rate that water vapor will transfer through a given substance.

Moisture transmission is a factor that is considered in the design of clothing, buildings, building components, and electrical equipment.

Safeopedia explains Moisture Vapor Transmission Rate (MVTR)

High levels of moisture vapor transmission are desirable in circumstances where a space is likely or guaranteed to get wet, and the transmission of moisture out of the space is necessary for proper drying to occur or to ensure the comfort of workers and reduce heat stress. In contrast, barriers to moisture transmission are a desirable means of protecting water-sensitive equipment or materials that react to the presence of water.

Various OSHA standards for electrical equipment and chemicals set limits on the amount of vapor allowed in an environment. This requires workplaces to erect high or low permeability moisture barriers that prevent moisture from entering an area or allow it to leave respectively.

The moisture vapor transmission rate is relevant to a broad range of workplace safety concerns. For instance, workplace hazard assessments may identify chemical materials that could be compromised by a high moisture environment and become hazardous as a result.

In office buildings in moist or humid environments, it is often inevitable that wall spaces and other niches will become wet. If these barriers have low moisture permeability and do not allow transmission of the moisture from inside the walls to cross into the larger environment, there is a risk that dangerous mold and rot could result. In some cases, this can result in large amounts of structural damage, particularly if the moisture collects into an increasingly large water deposit that degrades the structure it is trapped within. The moisture vapor transmission rate is also considered when designing personal protective equipment (PPE). High MVTR prevents employee discomfort due to moisture buildup inside the equipment.

Certain types of metals that are used in structural and electrical equipment can also be vulnerable to corrosion if they are not adequately protected from moisture by appropriate vapor barriers. This may result in electrical hazards or reduce the performance of protective equipment and other hazard controls.

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