Type I vs Type II ASTM D178 Matting: When Ozone, Flame and Oil Resistance Actually Matter

 Here's something most buyers don't realize until it's already a problem. ASTM D178 electrical matting ships as Type I by default. Ozone resistance, flame resistance and oil resistance aren't baseline properties that come standard, they're options that have to be specified at the time of order. A facility that assumes its matting handles all three because the data sheet mentions them somewhere usually finds out otherwise only after a electrical mat starts showing the kind of surface cracking that shouldn't happen this early into its service life.

What Type I actually covers and what it doesn't

Type I ASTM insulating mat is properly vulcanized elastomer that meets the dielectric and physical requirements for its voltage class, with moisture resistance built in. That's a real, tested baseline, not a stripped down version of the standard. It is the right choice for a clean, dry indoor panel room with no meaningful oil or ozone exposure nearby, which describes a large share of control rooms and standard switchboard installations. What it doesn't carry is any guaranteed resistance to ozone, flame or oil, so a room that has any of those three present needs to actively specify for it rather than assume the standard matting handles it.

The three properties that make up Type II, and why they're not one thing

Type II ASTM insulating mat isn't a single upgrade, it's three distinct properties, each tested and rated separately, and a facility can specify any one, two or all three depending on what the room actually has in it.

Type IIA covers ozone resistance, tested by checking for any visible effect on the surface after ozone exposure. This is the one that matters most often and gets requested least, because ozone generating sources, motors, transformers, generators, anything with continuous electrical arcing in normal operation, are common right next to the rooms where matting gets installed. The surface cracking that shows up on an aging mat near this kind of equipment is almost always a Type I mat sitting somewhere it needed Type IIA.

Type IIB covers flame resistance, tested for self extinguishing behavior within 30 seconds of an ignition source being removed, with a maximum allowed char height. This one matters less for routine shock protection and more for rooms where an arc event carries a real ignition risk alongside the electrical hazard itself, which is a different question than voltage class and worth asking separately rather than assuming it's covered by matting rated correctly for voltage alone.

Type IIC covers oil and water resistance, tested by limiting volume swell to a maximum after oil immersion. This is the most simple one to identify, since it's relevant anywhere mats sit near hydraulic equipment, oil cooled transformers  or a general industrial floor where oil contact happens routinely rather than as an occasional accident.

Specifying the properties a room actually needs, not all three by default

Because these three ratings are separate, a buyer doesn't have to choose between standard Type I and a fully loaded Type II. A room with ozone exposure but no realistic oil contact only needs Type IIA, and ordering the full combined rating adds cost without adding protection the room will ever use. The mistake runs in both directions though. Treating “Type II” as a single optional upgrade that sounds like overkill for a standard panel room is how a facility ends up skipping the one sub-rating, usually ozone resistance, that the room actually needed, simply because the whole category got dismissed together.

A simple way to check which ones apply

Before finalizing a ASTM electrical matting order, three questions sort this out. Is there ozone generating equipment, motors, transformers or generators, within the same room or close enough to matter. Is there an arc or ignition risk in this specific location that makes flame resistance relevant on its own, separate from the voltage class already being specified. And is oil contact at this location routine, from nearby hydraulic systems or oil cooled equipment, rather than an unlikely one off. Answering those three honestly, room by room, usually sorts out exactly which Type II sub-ratings are worth specifying and which ones would just be added cost for a hazard that isn't actually present.

A spec sheet that lists Type I and each Type II sub-rating side by side, alongside the voltage class already chosen for the room, turns this into a standard checklist rather than a guess made at the point of order.