This question may appear easy to answer, but in fact, is dependent on a host of factors. Here is Ecolink’s answer:

No “Perfect” Chemicals
There are no “perfect substitutes” in any attempt to reduce or eliminate hazardous solvents in the workplace. If there were, everyone would be using them! Every cleaning solution carries a matrix of risk factors for environmental, health or safety reasons. Inevitably, any chemical choice involves weighing the alternatives (or as some might call it: “selecting the less-bad choice.”)

The Hazard Ladder
Ecolink places every product within a “hazard ladder,” to help in the selection process for a particular application. While this hierarchy is both technical and subjective, it provides a sound foundation for evaluating alternative cleaning chemistry for a given application.

Relative Risks and Benefits
Keep in mind that the circumstances of your specific application will override any set of assumptions. The hierarchy below is relative to site-specific impacts and benefits related to a given chemical. Listed from top down with increasing levels of hazard:

The Ecolink “Environmentally Preferred Choices” Ladder

1 Avoid the Need to Clean
Find a way to keep the part from becoming dirty in the first place.
2 Modify the Part or Contaminant
Use no-clean flux, water based cutting fluids, etc. Clean with non-solvent based cleaning technology.
3 Use high pressure water or water-based cleaners.
Non-halogenated, non-flammable solvent technology.
4 Use terpene, aliphatic hydrocarbon, dibasic esters, etc.
Non-halogenated, flammable solvent technology.
5 Use alcohol, acetone, etc.
Non-ozone depleting, low toxicity halogenated solvents.
6 Use HFE and HFC blends.
Non-ozone depleting halogenated solvents.
7 Use N-Propyl Bromide, TCE, etc.
Non-ozone depleting halogenated solvents.

While there is no perfect chemical solution, Ecolink provides a proven strategy for moving your MRO chemical usage “up the pyramid ” toward less toxic products.