While the NEC permits the use of a Cl 1 Division 1 approved thermal mass flow meter in a Class 1 Div 2 location, the installation expense of the flowmeter is significantly higher and often overlooked when selecting the appropriate device for the location.

Class 1 Div 2 and 1 Refresher

Class 1 Div 2 has edge over Cl 1 Division 1
When selecting a thermal mass flow meter for a Class 1 Division 2 Hazardous Area, using a flowmeter with Class 1 Division 1 approvals increases installation costs, giving the Sage Prime an edge.

The Sage Prime® is rated for use in Class 1 Division 2 areas.  For a quick refresher on hazardous areas,

Class 1 means the presence of hazardous (hydrocarbon) vapors or gases.

Division 1 means that the hazardous vapors are frequently present.

Division 2 means that the hazardous condition infrequently occurs (such as in an emergency).

Many industrial facilities have classified their plant areas as Div. 2. This has been done primarily for two reasons:

  1. Environmental – A Division 1 area frequently has hydrocarbon vapors present which is not desirable with EPA requirements for fugitive emissions, greenhouse gases and potential fines.
  2. Expense – The installation cost is less expensive in a Div. 2 area because flexible conduit can be used and conduit seals are not required.

Determine the Classification of Your Thermal Flow Mass Meter

A Division 1 area requires the use of an explosion proof enclosure to contain any explosion while a Division 2 device requires a circuit that will not ignite the vapor/air mixture under normal operating conditions. Some of the leading thermal mass flow meter manufacturers are only categorized Class 1 Division 1, unlike the Sage Prime® which has a Division 2 rating.

Division 1 Device Increases Installation Costs

According to the National Electric Code Section 500.8(B) (2), explosion proof instruments rated for Class 1 Division 1 can be used in Division 2 areas; however, the device must be installed in accordance with Division 1 requirements. This means that the conduit seals and rigid conduit will need to be installed up to the seal.  This can significantly increase the installation cost, and it is likely that many customers do not consider this until installation time.


When selecting a thermal flow meter for installation in a Div 2 location, remember that using a meter approved for Cl 1 Div 2 will save on your installation costs.

Perhaps this video and the following articles may be of interest to you:

AIS Publishes White Paper on “Hazardous Areas Classifications

Broadway World-Oct 28, 2013

In North America, the method used is the “Class/Division” system with areas by zones and is further categorized by Divisions (I and II).

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