Q. Is there a threshold for placarding a trailer shipping compressed acetylene gas cylinders? I was told that if the cylinder and gas met or exceeded 1,000 pounds the trailer or vehicle transporting the cylinders would require placarding.
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A. The general placarding requirements at 49 CFR 172.504(a) require that a transport vehicle containing any quantity of hazardous material must be placarded on each side and end with the placards specified in Tables 1 (hazard class/divisions 1.1, 1.2, 1.3, 2.3, 4.3, 5.2, 6.1, 7) and Table 2 (the other hazard class/divisions) of this regulation. However, fortunately this regulation sets forth several exceptions, including the one to which you refer.
The exception mentioned in your question is found at 49 CFR 172.504(c) which allows an exception from the placarding requirements for shipments that contain less than 1,001 aggregate gross weight (i.e. the total weight of all hazardous materials and their packagings loaded on a single transport vehicle) of any Table 2 materials. Your hazardous waste, acetylene, is a Division 2.1 (flammable) material with the identification number UN 1001 and it is listed on Table 2 of 49 CFR 172.504. Consequently, as long as your cylinders of acetylene and any other Table 2 materials being transported with the acetylene weigh no than 1000 lb, the transport vehicle does not need to be placarded.
However, placards would be required when the aggregate gross weight is 1,001 pounds or more. For example, if 700 pounds of Hazard Division 2.1 (flammable gas) and 200 lbs of another material specified in Table 2 of 49 CFR 172.504 – let’s say Class 8 (corrosive material) – are being transported, no placard would be required. But if the weight of either of these two materials brought the shipment’s aggregate gross weight to 1001 lb or more, the vehicle would have to be placarded for both the Class 2.1 and Class 8 materials.