A.
First of all, Viscous flammable liquids such as paints, enamels, lacquers,
varnishes, adhesives and polishes having a flash point of less than 23℃ (i.e., PG II) may be assigned to PG III in conformity with the procedures prescribed in the UN Manuals of Tests and Criteria, Part III, subsection 32.3.

Determination of viscosity can be done by “Flow Cup Method”, i.e., measuring the flow time applying the three right columns of Table 3.3.B, i.e., [(Flow time in seconds), (Jet diameter), (Flash point)]. Even with a more severe flash point, and even if the diameter of the jet hole is wider, the fluid takes more time to flow through, i.e., it is far viscous and it would not easily catch fire and therefore may be treated as PG III instead of PG II.

If the “Flow cup method” to determine the viscosity is not suitable, then take the kinematic viscosity approach outlined in the left most column of Table 3.3.B.
Kinematic viscosity (Symbol “v” ) in mm2/s at 23℃ is indicated in the first
column. Even if the flash point of the viscous liquid is lower, the time required
to spread over 1 square millimeter of area takes longer time, i.e., the kinematic
viscosity is higher, and therefore it does not catch fire easily.

The viscosity thus determined may now allow the PG II substance to be treated
as PG III. The rule is being relaxed. It is not made more severe. The maximum net quantity per package is no longer the limits for PG II as shown in the DGR blue pages, but a new easier benchmark of 30L (for passenger aircraft) and 100L (for CAO aircraft) is offered in DGR 3.3.3.1.1. (d). You must note that the majority of rules in the DGR are restricting rules, but the viscosity rule is an unusual easing rule. You are allowed to ship more than the standard rule.

Let me post one example. UN1133 Adhesive Class 3 PG II Quantity 10L is to be shipped. It is viscous substances. You determine from the blue pages that UN1133 PG II is to be packed in PI353 with a maximum net quantity limit of 5L. Luckily this is viscous substance, so you can treat it as PG III and the maximum net quantity you can use is increased to 30L for passenger aircraft carriage. You can get the shipment going.