1660253847878 Hazardoushmihero

Which HMI is best for hazardous areas?

May 19, 2020
How can I interface with machinery in environments with combustible dust or flammable gas?

A Control Design readers writes: I work at a production facility that always has combustible dust present during processing and a few of the production plants always have flammable gas present. These multiple area classifications make it difficult to install human-machine interfaces (HMIs) near the production processes to control the processes, machines and conveyors.

I’m having a difficult time finding the hardware I need, so I have a couple of questions. First, what are my options for HMIs in these hazardous areas? Secondly, how do I install and operate HMIs in hazardous areas if I’m having trouble finding units that are safe to operate in Class 1 and 2, Div. 1 areas?

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Digital meters

I read with interest your reader’s problem of replacing obsolete analog meters in a hazardous location while operating with HMI digital display equivalents, as well as without making changes to the existing installation.

I’m aware of two solutions to this problem: use either an intrinsically safe meter or use an explosion-proof meter that meets Class I and II, Div.1 specifications.


Figure 1: Designed for nuclear/military customers, the SSAM is not only 100% powered by the signal, like analogs, but also detects and subsequentially alarms the user when the signal fails for more than one hour.

In 1974 my company was successful in producing the industry’s first 100% signal-power digital panel meter. Forty-eight years later at the request of a nuclear customer to avoid the expense of cybersecurity protection (NEI08-09) of out Class1E NTM series, we introduced the grandchild of the 516, which is 100% hardware only—no cybersecurity liabilities—the Solid State Analog Meter (SSAM, Figure 1). Designed for our nuclear/military customers, the SSAM is not only 100% powered by the signal, like analogs, but also detects and subsequentially alarms the user when the signal fails for more than one hour—no more stuck needles. In addition of visual indication, the SSAM can transmit the failure alarm via serial or wireless soon, has dual alarm limits to 240Vac, and can even retransmit a 4-20 mA signal. All loop-powered by a 4-20 mA signal, except retransmission and serial. I’m currently working on 1-5 mA current loops version. Why did we use only hardware? Designing the SSAM in such a way allows it to be considered exempt of cybersecurity (CS) hacking and related regulations and expenses. For CS compliance we make the SSAM’s twin, the New Technology Meter (NTM) series, which complies to the NEI08-09 mandate. Either the SSAM or NTM is now offering wireless options to eliminate the need for wiring/rewiring your I&C room.


Figure 2: explosion-proof NTM-X is available as intrinsically safe inside an explosion-proof housing

For applications where the signal is not capable of powering our powerless, presently we need less than 5 mW of energy and we are working on improving this threshold, and/or an application that contains power-hungry features—relays, powered retransmission—our explosion-proof NTM-X is available as intrinsically safe inside an explosion-proof housing (Figure 2). However, the signal and power must be off before connecting/mounting the unit or in a safe environment. The NTM-X offers relays, retransmission, serial I/O, signal fail alarm and other features IF externally powered, otherwise the powerless version is your best choice (Figure 3).

With and without housing

Figure 3: The NTM-X offers relays, retransmission, serial I/O, signal fail alarm and other features IF externally powered, otherwise the powerless version is your best choice.

OTTO FEST/ president / Otek


We’re working in the oil-and-gas market all around the world. Therefore we had to provide HMI suitable for hazardous location a few times.

Many HMI manufacturers are able to provide HMI suitable for hazardous locations in accordance with IECEx, ATEX and similar certifications or directives. These products could be installed directly in hazardous locations with a simple physical protection since they are already certified.


Chief sales & marketing officer / SEID / www.seid.it / Control System Integrators Association (CSIA) member

2 options

We have used one of two methods for HMIs in these environments—purged enclosures for the HMI. There is one company that makes them I am aware of, but typically we look at doing it ourselves in our panel shop. The other, which is much more cost-friendly, is to use hazardous-rated, battery-operated tablets. We just deployed three of these on a solvent-based compounding process and have a few names of manufacturers.

Bob Willems / business development manager / Sure ControlsControl System Integrators Association (CSIA) member

Avoid the area

The first thing to consider is whether the HMI and most of the control system can be placed outside of the hazardous area. This is the easiest way to achieve your goal and keep costs lower.

Another method that can be investigated for suitability in your environment are purge and pressure systems. These are systems where the sealed enclosure in the hazardous areas are first purged of any hazardous gas and then pressurized with laboratory-quality air or an inert gas. Part of this system prevents power from being applied to the enclosure until the enclosure is pressurized. The IEC recommends a minimum enclosure rating of IP40. However, UL Type 4 (IP65) enclosures can be used as they are robust and provide additional latching points that assist in preventing leakage. UL Type 12 (IP54) enclosures may also be used, but they may have a higher rate of leakage. Leakage can increase costs. An HMI can be used in this application if the front panel touchscreen will not bubble under the pressure part of the cycle. NFPA requires a minimum enclosure pressure of 0.1 inches of water column (25 Pa) for Class I and II applications. There are HMI screens available that can operate under this pressure without bubbling or affecting the touchscreen.

CLARK KROMENAKER / product manager—HMI, IPC, controllers, software / Omron Automation Americas

For safety’s sake

First off, if the combustible dust and flammable gas conditions are always present during normal conditions then Class I or Class II, Div. 1 enclosures will definitely be needed to protect the HMI. In these cases, I would still recommend using a Class I, Div. 2 HMI with wide temperature specs such as -20 to 60 °C such as the Uticor HMIs as a normal NEMA 4/4X HMI like those mostly on the market will not be as suitable for the environment. If the substance referred to by class is present only in abnormal conditions such as container failure or system breakdown, then you can get away with using an HMI that is just Class I, Div. 2 in a normal enclosure. I also recommend purged enclosures that can handle an atmospheric pressure above 1ATM if you really want to be safe. 

Particular to Uticor HMIs we are rated Class I, Div. 2 for hazardous environments that cover the following groups:

  • Group A: acetelyne
  • Group B: hydrogen (or gases of equivalent hazard)
  • Group C ethylene (or gases of equivalent hazard)
  • Group D gasolone (or gases of equivalent hazard)
  • Group E: metal dust
  • Group F: coal dust.

VIKRAM KUMAN / president and CEO / Uticor Technologies, a div. of AVG

Just a client

The user needs a purged enclosure for his HMI. The software solution architecture would likely be where the display at the equipment is just a client to a SCADA server in a server room.

PRASAD PAI / lobal industry and partner marketing director / GE Digital

Strongly consider a mobile solution

At the risk of being pedantic, an initial question to consider is whether you need a control interface and process visualization or whether control by itself is sufficient. I mention this distinction because there are many intrinsically safe components and explosion-proof options for basic control that might get you a good deal of the way to where you need to be with much less expense and headache. That said, since you are asking about HMI solutions, I’m going to assume you want the full package.

The traditional approach to this challenging design problem would be a purge and pressurization system for a fixed display. This approach is complicated for a number of reasons but prevalent because of a lack of suitable options for the environment you’ve described. The good thing about this option is that you don’t have to design the complete solution yourself. There are purge systems ready to deploy from manufacturers like Pepperl+Fuchs and Hoffman.

Since you are looking for the full package, though, I’m going to encourage you to take a serious look at a mobile HMI solution. In contrast to the traditional fixed operator interface, few mobile solutions have been available in the industrial space until the last few years, particularly for a hazardous environment like yours. That’s because a suitable design requires multiple complementary technologies, some of which are only recently coming to maturity.

A mobile design consists of three primary pieces:

  1. safety-approved wireless networking equipment
  2. safety-approved mobile devices
  3. mobile HMI/SCADA visualization software.

Depending on the age or upkeep of your field devices, it’s very likely that you already have this part taken care of, considering how Ethernet has proliferated into industrial communication. If not, though, there are mature product options available from the likes of Eaton and Pepperl+Fuchs for creating moderated intrinsically safe (IS) Ethernet, as well as explosion-proof housings for network gear, all rated for your Div. 1 environments. I use the term “moderated” because the tradeoff with IS Ethernet is that it imposes limitations on network speed. You likely will not achieve the gigabit speeds you have on your corporate network, but you will be able to deploy managed network switches and wireless access points within Div. 1 areas.

With the appropriate network infrastructure in place, it makes much more sense to protect a low-voltage electrical device like a handheld tablet or smartphone than a traditional HMI, and the quantity of IS mobile devices now available reflects that. These are not simply Grandma’s iPad in a shock-absorbing jacket, either. You can find devices from ECOM and others that include Zone 1, Div. 1, and MSHA approvals. Their ability to safely run a web browser or mobile apps anywhere in your facility sets you up for the final part of the solution.

Mobile visualization has been the primary missing link keeping a solution like this from taking off. Now that it’s here, it needs very little explanation because who doesn’t use a smartphone? You have seen so many consumer and even enterprise applications capable of running on a mobile device that you’ll wonder why your HMI hasn’t been available on your phone for years.

There are mobility options available. They allow you to build displays, typically in a Web browser, connect those displays to various data sources in your facility, and then visualize those displays from any HTML5-compliant Web browser or via native mobile apps on devices connected to your network. You can opt for server-based deployment or for embedded options that run directly on a PLC or industrial edge controller.

The trade-offs with this approach are that you will be on the cutting edge of process visualization, and you will need to work closely and amicably with your local IT group to ensure that data and signal integrity are sufficiently managed. You will also need to consider the importance of cybersecurity features—for example, HTTPS, user authentication, certificate management—as you evaluate these options. However, since it is much easier to add additional HMI in this design than with traditional fixed displays under purge, you can reasonably expect up-front investment and ongoing maintenance to be significantly lower, depending on the scale of the system.

JOSH EASTBURN / director of technical marketing / Opto 22

Paradigm shift

The simplest solution in your Class I, Div. 2 rated areas is to use a Class I, Div. 2 rated HMI. When it comes to Class I, Div. 1 areas it gets more complicated. The presence of combustible gas requires much more consideration. A shift in traditional thinking may be what you need to succeed in your application. Does your application need an HMI in the traditional sense?

A screenless HMI might be the option you need. A screenless HMI can be housed within the enclosure and the enclosure can be purged to UL standards. With the screenless HMI connected to your network, the HMI could then be accessed via PC, tablet or mobile device from a safe location out of the classified area. Or a classified mobile device could be used to access the HMI within the area. Both these options allow for the operation of the HMI as if you were at the machine.

This shift in thinking allows for a truly flexible solution for your production facility that is also very cost effective.

KEITH MOYER/ vice president of sales / Weintek USA

Class and div.

There are many Class I, Div. 2 HMIs, far fewer Class I, Div. 1 HMIs. Due to the design and components used in building these hazardous HMIs, Class I, Div. 2 approved products tend to have higher costs than non-approved products; Class I, Div. 1 HMIs have a much higher cost than Class I, Div. 2 HMIs. For this reason and where reasonable, the HMI is usually located in a non-Class I, Div. 1 environment, often only requiring a movement of a few meters. This also makes it safer for the operators when this placement is reasonable.

In the United States and Canada, having third-party approved products, such as through UL or cUL, imply Class I, Div. 2 approvals as set forth by the U.S. National Electrical Code and the Canadian Electrical Code. In Europe, the approval is usually ATEX Zone 2 and in other parts of the world, IECEx Zone 2. All of these involve situations where the gas is not normally present but may accidently exist. Class I, Div. 1 environments (or ATEX Zone 1 or IECEx Zone 1) are where the existence of explosive gas is normal. The former is quite common in the deployment of industrial electrical systems including HMIs, the latter less common.

Dust is a bit different as the standards are Class II, Div. 1 (dust normally present) or Class II, Div. 2 (dust accidently present), ATEX Zone 22 and IECEx Zone 22. There are also Class III (Div. 1 and 2) approvals for fibers and flyings, such as those found in textile and wood mills. Few HMIs have formal dust or flying fiber approvals because many assume the gas approvals will suffice.

Realize the HMI is just one electrical component that exists in a hazardous location. One also needs to consider the PLC, the I/O, the data networking switch, and other components found in an electrical panel. Some of these are also approved for hazardous location , quite a few Class I, Div. 2 products, much fewer Class I, Div. 1 products.

JEFF HAYES / regional product manager / Beijer Electronics

Flexibility in design

Luckily, there are a few options for HMI operation in both Div. 1 and Div. 2 areas.

Since the potential hazard is not always present in Div. 2 areas, the design and restrictions for HMI are not as stringent as they are for Div. 1. Many manufacturers make properly rated HMI in various mechanical designs for Class I and Class II, Div. 2 locations. These include fully enclosed workstations that mount onto a wall arm or pedestal and panel-mount designs that mount into an enclosure or cabinet. In most cases, the designs account for a specific degree of protection or type rating (IP66 or Type 4X, for example).

More complex HMI solutions are required for more severe Div. 1 locations. This limits the number of potential vendors who can provide an appropriately rated product. The only suitable protection methods for Div. 1 classified areas are intrinsic safety, explosion proof, and purge and pressurization. However, it is not feasible to design the HMI-specific components (motherboard, hard drive, memory) using intrinsic safety or explosion-proof protection concepts because of power requirements and temperature considerations. This means that purge and pressurization is the only viable protection method for Div. 1 HMI solutions.

For these purged Div. 1 HMI solutions, the unit must undergo the proper purge and pressurization process prior to energizing the HMI. For Class I (gas), Div. 1 applications, the solution must complete a full purge cycle where forced air pushes the hazardous gases out of the enclosure. Once the purge cycle is complete, the system can then provide constant pressurization inside the enclosure, keeping the hazardous gases out while the system remains energized. For Class II (dust), Div. 1 applications, dust that has accumulated on the solution’s internal electronics must be cleaned off. Once the dust has been cleaned off properly, the system can be pressurized to prevent further dust ingress.

In solutions for both Div. 1 and Div. 2 locations, numerous HMI technology concepts can be used to run the applications and process software that the installation location requires. This gives the customer a ton of flexibility in design implementation. Examples include:

  • systems with a full PC running Windows operating system where programs and applications are installed locally
  • thin client design where the HMI system is networked back to a host PC or server via a remote connection protocol (Microsoft RDP, for example)
  • keyboard, video, and mouse (KVM) design concept where a KVM transmitter and receiver are used to remotely connect to a host PC.

In summary, while limited in quantity, there certainly are manufacturers and design concepts for HMI workstations within hazardous locations.

AARON SEVERA / product manager—HMI, FieldConnex, Remote IO / Pepperl+Fuchs

Sensing to visualization

While there are several options for operator panels in Class I, Div. 2 spaces, flammable gas or liquid with low chance of ignition, true Div. 1, high combustion risk, solutions are harder to come by. A good solutions partner in the hazardous location space will offer everything from sensing to visualization in Class I (liquids and gasses) and II (dusts), Div. 1 ratings.

JIM DAVIS / director of advanced solutions & technical support / Allied Electronics & Automation

About the author: Mike Bacidore
About the Author

Mike Bacidore | Editor in Chief

Mike Bacidore is chief editor of Control Design and has been an integral part of the Endeavor Business Media editorial team since 2007. Previously, he was editorial director at Hughes Communications and a portfolio manager of the human resources and labor law areas at Wolters Kluwer. Bacidore holds a BA from the University of Illinois and an MBA from Lake Forest Graduate School of Management. He is an award-winning columnist, earning multiple regional and national awards from the American Society of Business Publication Editors. He may be reached at [email protected] 

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