Environmentally preferred alternatives to chlorinated solvents and their proper usage
For several decades, electrical maintenance cleaning and degreasing was done with chlorinated solvents, first using carbon tetrachloride, and then switching to the less toxic 1,1,1-Trichloroethane (also called methyl chloroform, trichlor, or TCA). Aerosol cans, wiping pads, and small bulk packages of trichlor and trichlor blends were common for electrical cleaning.
This chlorinated solvent was used in electrical maintenance for motor refurbishment and cleaning bushings and breakers. Since production and importation of 1,1,1, trichloroethane is now banned in the United States; there is a need for alternative electrical cleaning solvents. Several alternative solvent systems have been developed and used successfully in electrical cleaning. In the United States, slower drying petroleum distillates have worked well. In Europe, isopropyl alcohol (isopropanol) has been used. Occasionally, the more toxic chlorinated solvents perchloroethylene and trichloroethylene are seen.
To analyze alternative electrical cleaners, we must first understand their key functional properties.
“Evaporation rate” can be determined in several ways. A crude but simple measurement involves placing a measured quantity of the solvent in a container (open), and determining weight loss over time. Evaporation is in milligrams/minute at a given temperature and solvent configuration (surface area to volume).
To understand how slower drying solvents are best used in the field; remember that the evaporation rate of a solvent is dependent on “configuration” (volume versus surface area) and temperature. The cleaning procedure should “dry” the cleaner to a very thin film and then allow time for evaporation.
In the United States, all liquids with flash points under 93°C (200°F) are regulated for shipping purposes. Liquids with flash points under 38°C (100°F) are called flammable liquids and are the most restricted. The point is that low flash point solvents must be handled with knowledge and care for both legal and safety reasons.
There is no single answer to the evaporation rate/flash point dilemma. Evaporation properties in the field not only depend on the cleaner, but also the ambient temperature and cleaning procedure. Different users will resolve the replacing chlorinated solvent dilemma in different ways. Evaporation rate is only one property of cleaners.
A good electrical cleaner should not leave a “residue,” that is, some part of the cleaner that does not evaporate. A residue could provide a path for tracking or potentially interfere with the electrical function of the part.
Some “degreasing” solvents available to the electrical industry contain “surfactants.” These surfactants are left as residues, and cleaners containing non-volatile surfactants should not be used for electrical cleaning. Occasionally a user will conclude that a slower drying cleaner leaves an “oil residue.” High purity slow-dry solvents do dry completely; they just don’t do it quickly.
Electrical Cable Cleaning
Solvent cleaners are used when splicing electrical cables to remove contaminants that could provide a path over the insulation for tracking. Insulation shield residue, semi-conducting coating, inhibitor contamination, and other grime from handling are commonly removed.
Frequently, a failed splice is opened to reveal tracking that follows a “fingerprint pattern” of contaminants left during handling. An effective cleaning solvent removes such contaminants to eliminate any electrical path. The solvent itself, of course, must completely evaporate and not leave any residue of its own.
Unfortunately, not all solvents are equally “effective” at removing typical contaminants. One way to measure “effectiveness” is to saturate a white cloth with the solvent, and then wipe black semi-conducting shield residue from insulation. After a few wipes, the amount of “black” (semi-conducting material) picked up by the cloth varies significantly, depending on the solvent. In our testing, we rated it from a zero (no visible black residue on the cloth) to ten (a lot of residue picked up very quickly).
How do these same solvents affect cable or splice materials? Based on the way they’re used, the primary concern with cleaning solvents has been their effect on semi-conducting materials. These semi-conducting polymers are very sensitive to solvent migration, which disrupts their carbon black network and raises their resistivity.
An evaluation method used by some utilities and cable manufacturers has been to immerse the semi-conducting material in the solvent to measure the volume resistivity effects. If we choose a solvent that has no effect on the volume resistivity of the semi-conducting polymeric materials, we’ll choose a solvent that won’t clean the residue of these same materials from the insulation. And if it doesn’t clean the residue, it leaves a potential path for tracking and splice failure.
To understand this, consider how cable is cleaned. No cable, splice, or connector manufacturer recommends, “immersing” cable in solvent. In fact, it’s just the opposite, and we can see why. A minimum amount of solvent should be used to wipe residue from the cable insulation. Puddling, direct spraying, dipping, etc., should be avoided.
Field users’ primary exposure to solvents is via inhalation (lungs). Because electrical cleaners evaporate, there are airborne vapors and a breathing exposure to the vapors.
Things we inhale can be toxicants or asphyxiants. Carbon monoxide (auto exhaust) and hydrogen cyanide (gas chamber) are examples of toxic gases. Gases like helium and nitrogen are asphyxiants. If they’re not mixed with enough oxygen, they can smother us. Obviously, life-sustaining oxygen is neither a toxicant nor asphyxiant. How do solvent vapors fit and how is their toxicity determined?
Toxicity of Vapors & Gases
What we need to know about airborne vapors is whether, and under what conditions, they’re “safe.” Industrial hygiene groups have answered this question, and established “safe working levels” for vapors or gases in air (40-hour-per-week exposure). These are called “Threshold Limit Values” (TLV’s) or “Permissible Exposure Limits” (PEL’s). TLV’s describe the maximum recommended working level for an average human. They are “concentrations” in air, and are most often given as parts per million (ppm). One ppm is .0001 percent by weight in air.
What Creates Solvent Vapors?
The concentration of solvent in the air in a closed environment (vault, room, etc.) is determined by the following factors:
- Size of enclosure.
- Speed of the solvent evaporation.
- Amount of solvent used (evaporated).
- Vapor dispersion (concentration areas in the vault).
- Ventilation (natural or mechanical, including efficiency for solvent type and room shape).
Individual examination of these factors will show how we can control them for safer solvent use.
If solvent vapor levels are above safe working maximums, ventilation or protective breathing canisters may be needed.
Several ways to control solvent exposure:
- Choose a less toxic solvent (higher TLV).
- If necessary, use mechanical ventilation to reduce vapors to safe working levels.
- Use the minimum amount of solvent needed to do the job; i.e., restrict quantity released.
- Choose as slow an evaporation rate as is practical for the timely completion of the task.
- Establish methods minimizing solvent exposure, including removing the used rag from the enclosure.
Choices for Electrical Cable Cleaning
ECOLINK offers several solvents that meet the objectives detailed above. The most popular products for cleaning prior to splicing are ELECTRON and POSITRON. ELECTRON is packaged in wipes, specifically intended for this purpose:
Ecolink Electron Cable-Cleaning Tandem Wipes
Ecolink’s Tandem Wipes accomplishes the above objectives. Each package contains a precisely charged minimum amount of solvent with relatively high TLV’s. Ecolink’s environmentally preferred solvents and cleaners are available with different evaporation rates for specific field needs. Ecolink has the expertise to adapt to your specific situations. Just ask if interested.