Equipment for Use in Potentially Ignitable Atmospheres

4524 Reactor with Aluminum Block Heater
Model 4524 Reactor, 2000 mL, Fixed Head Style with Aluminum Block Heater

Parr reactors are typically equipped with totally enclosed variable speed motors, electric heaters, and controllers intended for use in non-hazardous environments. These standard units can be used in most laboratories without undue hazard, but there will be situations where the installed equipment must be considered for use in ignitable atmospheres. Parr offers various optional stirrer drives and heating solutions to meet these strict requirements.

USA and Canadian Codes (HAZLOC – Hazardous Locations)

Designing electrical equipment to be operated in hazardous locations is a complex subject, which is governed by extensive national electrical codes and supplemented by local regulations. These codes require all electrical equipment that is installed in a governed location must be approved for use with the specific gas, vapor, or dust that can be present in the defined location. USA and Canadian electrical codes classify hazardous locations according to the nature and concentration of specific hazardous or flammable materials. These are divided into three classes:

Class I – Flammable liquids, gases or vapors.
Class II – Combustible or electrically conductive dusts.
Class III – Easily ignitable fibers/flyings.

There are two divisions within each of these classes.

Division 1 – Where the flammable material exists in the atmosphere under normal operating conditions.
Division 2 – Where the hazardous material is confined within a closed system from which it may be released only under abnormal conditions, such as a gas leak in the system.

Class I locations are further subdivided into four groups, A, B, C and D which identify specific explosive gases and vapors. Explosive dusts and fibers in Class II are subdivided into Groups E, F and G. Most hazardous applications for Parr apparatus will occur in atmospheres identified by Class I, Group B for hydrogen and Groups C and D for most other combustible gases and vapors. Class II, Group F covers coal dust. Most other combustible dusts, such as flour and grain, are in Group G. Minimum ignition temperatures and energy levels are established for specific materials in each group.

The European Community has corresponding classifications for “Explosive Atmospheres” referred to as ATEX (ATmospheriques EXplosives). Parr will work with all users to provide equipment compatible with their own local codes.

The components in Parr reactor systems that may be considered hazardous and the steps that can be taken to reduce or eliminate the hazards they represent are described below.

Air Motor
Air Motor


Because of sparking from brush contacts, permanent magnet DC electric motors clearly represent the principal ignition source introduced by a stirred reactor. Electric motors approved for Class I (Divisions 1 & 2), Groups C and D, and Class II (Divisions 1 & 2), Groups F and G atmospheres are readily available in most sizes and voltages. These totally enclosed motors are suitable for many hazardous applications, and they are sometimes used with hydrogen, though they are not approved for Group B atmospheres. Currently, there are no Division 1 motors available for Group A or B atmospheres. A special air purging system can be used to reduce the classification inside the motor. The motor is pressurized by building up a positive pressure of air, or inert gas, within the motor to prevent explosive gases or vapors from entering the motor housing.

Division 2 requirements are not as stringent. Other motor options are available. Please contact Parr for additional information for Class I, Division 2 requirements.

Parr can provide ATEX rated, IEC framed, AC motors when required. These constant torque motors have lower speed and torque characteristics than the DC motors Parr has used in the last several years.

An alternate method of dealing with the explosion hazard is to use an air driven motor. These are powered by compressed air and offer a convenient and satisfactory drive system for use in flammable atmospheres, including hydrogen. They are available in sizes suitable for most Parr reactors.


The advisable way to heat a Parr reactor in a potentially ignitable atmosphere is to use a hot oil jacket and ensure that the highest temperature of the heat transfer media is below the minimum ignition temperature for the classified area in which it will be installed.

Purging Parr’s aluminum block heaters with air, as well as limiting surfaces temperatures below the autoignition temperature, can make them suitable for use in classified areas, but it is likely that the air consumption in such heaters will be quite large. Please see our Heaters page for additional information.


Parr will provide ordinary location wiring for motors and heaters, which can be used for initial testing, setup, etc. Due to national and local requirements for installation of such equipment, it is the user’s responsibility to install mains and motor wiring per code requirements.

Parr will provide wiring for intrinsic safety related sensors, transducers, etc. For application specific information on sensors for use in hazardous locations, please contact Parr Instrument Company. See the handbook Understanding Hazardous Area Sensing – Intrinsic Safety from TURCK Inc. for a definition and enhanced understanding of the technology.


The most commonly used method for dealing with the ignition hazard introduced by a temperature or process controller is simply to locate the controller outside of the hazardous atmosphere. Another choice is to install the controller in an explosionproof cabinet or a cabinet that can be purged using the purging system described above.

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