What Is a Toxicity Rating (PEL, TLV, AEL)? Which Solvent Is the Safest (Has the Least Toxicity)?

At MicroCare, nothing is more important than safety. An important part of a strong safety program is understanding “toxicity ratings” for chemicals. This FAQ explains toxicity ratings and suggests how savvy engineers can use this information to improve safety in their facility.

What is a Good Score?

In the solvent world, chemists measure chemical safety in terms of toxicity ratings. These usually are called TLV (“Threshold Limit Value”, PEL (“Personal Exposure Limit”), AEL (“Assigned Exposure Limit”) or similar terms. These terms are generally (but not exactly) synonymous, and these rating systems work in the same general manner.

Note that these ratings are different from the popular NFPA ratings often found in the USA. Toxicity ratings are expressed in parts per million of chemical exposure. Like bowling, a high score is better and safer. It means you can be exposed to more of the chemical without any adverse effect. The scores are designed to estimate worker risk from exposure to the liquid for eight hours per day, five days a week, for a hypothetical thirty-year working career. A lower score means even a brief exposure to the cleaner may pose health hazards. A relatively hazardous liquid might have a TLV of 5 or 10 ppm. A safe fluid would be 400 ppm or higher. The highest possible rating is 1,000 ppm.

Field tests at MicroCare have shown that uncontrolled aerosol users are exposed to 75 ppm in normal use. TriggerGrip™ users and vapor degreaser users generally are exposed to 10-15 ppm.

MicroCare Uses Independent Toxicity Ratings

The best quality ratings are assigned by an independent safety organization ACGIH. Their toxicity ratings are based on data derived from very systematic testing protocols on animals. The actual lab results are then adjusted by trained hygienists and toxicologists to simulate a constant exposure to the solvent for hypothetical working career.

There are different types of TLVs, as well. MicroCare and most of the industry use “8-hour Time-Weighted Average” exposure ratings. There are longer and shorter and even instantaneous TLVs. Most of those are not relevant to cleaning fluids.

A “Rule of Thumb” About Toxicity Ratings

There is a good rule of thumb about TLV ratings. Toxicity ratings of over 400 ppm would be generally safe under most industrial situations. Isopropyl alcohol, also called rubbing alcohol, is a good benchmark. Super-pure, anhydrous IPA is available from MicroCare as the IPA-Based Flux Remover – IsoClean™ (#MCC-BAC) . It has a TLV of 400 ppm and a familiar aroma. While it is not a very powerful cleaner, it certainly isn’t going to make anyone sick.

Ratings from 100-400 ppm should require the product to be managed carefully. Ratings under 50 ppm are generally “pushing the envelope” and those chemicals should be used with caution.

It goes without saying that “toxicity” is NOT a perfect description of safety. Other important factors, such as flammability, storage, handling and disposal, need to be included in any safety analysis. Before selecting a solvent, contact a safety expert if you are unfamiliar with these issues and worried about the implications. Whenever the data is available, MicroCare uses ACGIH toxicity ratings. When that data is not available, MicroCare uses the toxicity ratings assigned by the solvent manufacturer. If that is not available, MicroCare lists all the toxicity data on the ingredients of each solvent within the MSDS sheet.

Good Solvent Choices with High TLV Ratings

If you like alcohol cleaning, we recommend Alcohol-Enhanced Flux Remover – ProClean™ (#MCC-PRO) which is a blend of three alcohols. It offers stronger cleaning than IPA with an improved safety rating of 568 ppm.

The No-Clean Flux Remover – VeriClean™ (#MCC-DC1) has a TLV of 200 ppm which sounds a bit on the low side, but in this case the TLV doesn’t tell the whole story. VeriClean™ is a remarkable solvent, based on siloxanes, and it is highly effective on most “no clean” fluxes and pastes. It is unique in that the raw material is quartz, also known as sand. (Yep, we mean S-A-N-D, as in high tide, sunburn and beach blanket bingo.) As for safety, the SDS sheet for the raw material says “No first aid should be required.” You don’t get much safer than that.

The nonflammable choices improve on worker safety even more. Choices like the General Purpose Flux Remover (#MCC-FRC), Heavy Duty Flux Remover – SuprClean™ (#MCC- SPR), the Lead-Free Flux Remover – PowerClean™ (#MCC-PW2) and so on) have very good toxicity ratings. Most of them have assigned TLV ratings in the range of 200 ppm. But in addition to being relatively safe they also are nonflammable. They dry quickly, have very little odor, have excellent materials compatibility profiles and some of them are azeotropes and so they can be used in heated cleaning systems.


Specific details about each product and its toxicity ratings can be found on every product specification sheet and in every safety data sheet (SDS) as published in this site.

MicroCare also recommends companies improve safety by improving the cleaning processes. This means to create a workplace environment where people use less solvent. MicroCare recommends using the TriggerGrip™ dispenser. in detailed field trials, the TriggerGrip™ dispensing system kept solvent vapors down to about 15 ppm, which improves worker safety. With the TriggerGrip™ dispensing system you will always use less solvent, get less on your hands, less in your lungs and less in your eyes. In this case, less is more — much, much more.