Hazardous classification of outdoor spraying

[Jimmy B]

I have a question about outdoor spraying. I'm working on a custom made blasting/coating robot but I want to be sure about the requirements for the equipment. I'm assuming all the servo motors on the machine will need to be Zone 1 explosion proof, but what about nearby electrical equipment (ie. the control panel)?

Referencing Canadian Electrical Code, 20-302 says that any spraying not conducted in spray booths has a Zone 1 area 6m around it, and a Zone 2 area to "the edges of the building". This could be reduced if there was "adequate ventilation with effective interlocks provided at floor level", so that the Zone 1 area is only 1m away from the spraying and the Zone 2 area is 6m.

What's the classification here for outdoor purposes? Can I assume that being outside is an effective interlock and use those limits? Does being outside derate it even more and I can use general purpose outdoor equipment? I'm not sure, any advice would be great.

Even if you aren't familiar with Canadian code, I would be happy to hear about the NEC, since there is a lot of overlap between the two. Thanks!

 

[rbalex]

The problem, such as it is, is defining the “spray area”. It was well-defined in Section 516.2 in the 2017 NEC. It’s harder to find in 2020. In any case, once it is determined for an unenclosed location the “spray area” itself is Division 1. All locations 20’ (6M) horizontally and 10’ (3M) vertically beyond the “spray area” Is Division 2.

The Spray Area is defined as:

Spray Area.
Any fully enclosed, partly enclosed, or unenclosed area in which dangerous quantities of flammable or combustible vapors, mists, residues, dusts, or deposits are present due to the operation of spray processes, including (1) any area in the direct path of a spray application process; (2) the interior of a spray booth, spray room, or limited finishing workstation, as herein defined; (3) the interior of any exhaust plenum, eliminator section, or scrubber section; (4) the interior of any exhaust duct or exhaust stack leading from a spray application process; (5) the interior of any air recirculation path up to and including recirculation particulate filters; (6) any solvent concentrator (pollution abatement) unit or solvent recovery (distillation) unit; and (7) the inside of a membrane enclosure. The following are not part of the spray area: (1) fresh air make-up units; (2) air supply ducts and air supply plenums; (3) recirculation air supply ducts downstream of recirculation particulate filters; and (4) exhaust ducts from solvent concentrator (pollution abatement) units. [33:3.3.2.3]

Informational Note: Unenclosed spray areas are locations outside of buildings or are localized operations within a larger room or space. Such are normally provided with some local vapor extraction/ventilation system. In automated operations, the area limits are the maximum area in the direct path of spray operations. In manual operations, the area limits are the maximum area of spray when aimed at 90 degrees to the application surface.

 

[Jimmy B]

Awesome, that's very helpful! I used that reference to find NFPA 33, which definitely helps shed light on the situation. With the NEC/NFPA, it's very clear that an outdoor application is an unenclosed spray area and I could just use this figure:


However, the CEC complicates the matter because I need to use two different figures for unenclosed areas. One with the ventilation interlock, one without:


If I can assume that I can use CEC diagram 6 because being outside is a sufficient "ventilation interlock", then it's pretty clear. Otherwise, using Diagram 5 the Zone 2 area continues to infinity...

However, I was prompted by the NFPA reference to look at the Canadian fire code (NFC 5.4.5.2), and it just states:

The design, operation and maintenance requirements relating to spray coating processes shall conform to NFPA 33, “Spray Application Using Flammable or Combustible Materials.”

With that in mind, I'm feeling pretty good that I can use the the 20'/6m limit for Zone 2. I have to confirm with the local safety authority to be sure.

 

[rbalex]

You have just discovered that Zone 1 is just a slightly upgraded Division 2 AND Canada uses IEC “full-blown” in preference to typical US standards for hazardous locations.

 

[Jimmy B]

This is the consequence of literally taking two very different systems, slapping them together and hoping like hell it will work out!

 

[rbalex]

This is the consequence of literally taking two very different systems, slapping them together and hoping like hell it will work out!

I agree. My personal opinion was - IF the NEC was to adopt “Zones”, we should have done it as Canada did; i.e., adopt it ‘whole-hog.” Instead we attempted to force-fit IEC Zones into a Divisions philosophy. I spent about a third of my career engineering to IEC (and its coresponding international Standards). I told the NFPA that mass confusion would ensue. After over 20 years, it still hasn’t cleared up.