Recently my team has been engaged in conducting wireless surveys in process environments and I thought this would be a good opportunity to post what I have learned in this area since the internet does not do a good job of breaking down the options. This is definitely not a full course on hazardous environments. The intent of the article is to provide some guidance when the need arises for installing a WiFi access point in a classified environment.
Many manufacturing areas or petroleum refineries have areas that are classified as hazardous. A hazardous area typically has gas, dust, or fibers that are highly combustible. Shown below is a table showing the environmental classifications as defined by NEC Article 500. The different classes are broken up into each type of combustible material as well as how likely the material is to be found in the environment.
The equipment that is operated in these areas must be rated according to these areas. Failure to do so increases the likelihood of an explosion that would really ruin your day (probably life). ☹
Typical ignition sources are sparks caused by motor windings or switches or it can come from a heat source like a lamp or a bearing. Other ignition sources can be a shorted or damaged electrical circuit. Everybody remembers the phone batteries and their overheating issues. These could definitely set off an explosion and should not be allowed in the area unless they are rated Intrinsically Safe or I.S. and the rating must match the environment they will be in. Wikipedia’s definition of Intrinsically Safe is “a protection technique for safe operation of electrical equipment in hazardous areas by limiting the energy, electrical and thermal, available for ignition.”
Often overlooked is the fact that WiFi surveys cannot be performed in these environments in the normal way. The access points and electronic survey equipment normally used is not rated for these environments and may cause an explosion. This does not mean we cannot do it however. Hot-Work permits can be created by the manager or supervisor and safeguards can be put in place to prevent a catastrophe. More importantly, gas monitors can be utilized by the surveyor (or the escort) to determine whether or not there is any risk. This is often overlooked but I highly recommend this for obvious reasons.
Having said that, too often WiFi surveys in hazardous areas are done in a haphazard way (see what I did there? 😊). Due to the limitations the surveyor will choose to skip an APOS and decide (guess) where the access points should go. These are typically the areas where the APOS really needs to be done. Even if you can only survey part of the environment, you can get an idea of the propagation characteristics and make better decisions based on that. Surveys in hazardous areas can be done safely so I recommend surveying as much as possible until you get a pretty good idea for AP placement.
There is not a whole lot of information on the internet about how to install access points in an enclosure and what the requirements are. Sure you can find plenty of access points that are certainly rated for gas environments however the Class 2 environments is a different story. Many people assume you can install an AP that is rated for a Class 1 area in a Class 2 area but this is not true. Please do not install a Class 1 AP inside a Class 2 environment as this is unsafe. It is kind of funny because I know I have directly asked manufacturer reps in meetings and sent emails regarding what they recommend for dust environments and all I get back is usually a statement saying they will look into it and that they know somebody that can help but in the end I don’t get anywhere. The quick response is to install the AP in an explosion-proof enclosure that costs many thousands of dollars. This article will hopefully shed light on Class 2 environments and how to possibly save some money.
The very first thing you should do is to verify the classified area absolutely needs WiFi coverage. After verifying I recommend the following:
- Try to find an MCC (Motor Control Center) or an area that is adjacent to the hazardous area needing to be covered and evaluate whether or not an AP can be mounted in this area. If possible, then place a test AP in this area and conduct a quick measurement of the signal in the hazardous area. You may want to use a higher gain (directional) antenna to maximize coverage in the hazardous area. If sufficient coverage is provided by the AP, then you have your answer and avoided a more expensive option.
- If the coverage is insufficient then another option is to mount the AP in the unclassified area and run antenna cables through the wall and mount the antenna (directional?) on the other side of the wall. The important thing here is too ensure you install an RF barrier to prevent any excess energy from being able to propagate down the antenna line and potentially cause an explosion. These barriers can be found at Solexy.net and they are made specifically for these applications. See below:
The options above will save you money however if none of these options will work, we need to start considering mounting the AP in the area or within an enclosure that is rated for the environment. I will break this down into Class 1 (gas) environments and Class 2 (dust) environments. The environmental temperature also becomes a concern and needs to be included in the solution. If the environment is hot or cold, it is important to understand the operating temperature of the access point. Outdoor access points typically have a much wider operating temperature range (-40°F to > 150°F) than indoor or office access points.
Class 1 Div 1 – there is likely a sufficient amount of gas in the area to cause an explosion
The only option in these highly explosive environments is to mount the AP in an explosion-proof enclosure. These enclosure will literally contain an explosion and not allow sufficient heat to be transferred into the classified area. This is an expensive solution but thankfully the rarest (in my opinion). Here is a link to a popular company that provides these types of enclosures.
Class 1 Div 2 – there can be a sufficient amount of gas in the area to cause an explosion but it is abnormally present
Option 1) Cisco has recently come out with their new IW6300. The AP itself (when properly installed) can live directly in the environment. Here is the link to the spec sheet. This AP will set you back several thousand or more but also keep in mind the price to install it (conduit, etc.). The RF barriers I mentioned earlier are built in which means you can install any passive antenna you desire (within regulations). It is a clean option however in the end it may be just as cost effective to install an explosion-proof enclosure.
Option 2) Install an AP in an explosion-proof enclosure – same as Class 1 Div 1
Class 2 Div 1 – there is likely a sufficient quantity of dust in the air and any heat source can trigger an explosion or dust buildup that can also cause a heat buildup can trigger an explosion if equipment is mounted in the area without adequate protection
Option 1) Mount the AP in a Nema 9 enclosure (ignition proof) with external antennas that is separated with RF barriers. Again, there may be some cost savings here but in the end it is good to get a quote for an explosion-proof box as well as this option. See the picture below:
Option 2) Install an AP in a pre-built Class 2, Div 1 rated enclosure made by Extronics. They should have an enclosure and AP combo just for you.
Class 2 Div 2 – there can be a sufficient amount of dust in the area to cause an explosion but it is abnormally present
Option 1) Finally this is one class we can save money on! All that is required in these areas is to have the AP mounted in a Nema 4X box that is dust proof. A polycarbonate box can be purchased for ~ $150. Here are two variations of this box:
I hope this article has provided some guidance and helps fill in some holes or at least steers you in the right direction to be able to find more answers. I have also placed some links that have helped me understand the standards and definitely provide much more information. Feel free to ask any questions or post your comments. There is so much to learn in this area and I welcome anybody who has more guidance to offer. Thanks.
https://en.wikipedia.org/wiki/Electrical_equipment_in_hazardous_areas
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