What are WEL/OEL limits

WELs (Workplace Exposure Limits) are occupational exposure limits (OELs) which are set to help protect the health of workers, but, they are not levels above which harm will definitely arise and they are NOT levels below which harm will not arise. WEL's/OEL's do not address safety issues such as flammable concentrations. They are the measurement of concentrations of hazardous substances in the air, averaged over a specified time referred to as a time-weighted average (TWA).

There are two time periods used a long term, over an 8 hour reference period, and a short term, over a 15 minute period. The short term (STELs) are set to help prevent effects, such as eye irritation, which could occur after a few minutes.

UN transport codes

These codes are from the “ UN Model Regulations on the Transport of Dangerous Goods ”, they are not obligatory or legally binding on individual countries, but they have a wide degree of international acceptance and form the basis of several national laws and international agreements.
They include a classification system for substances that pose a significant hazard in transportation by air, sea, rail and inland waterways. The hazards addressed include explosive, flammability, toxicity (oral, dermal and inhalation), corrosive to human tissue and metal, reactivity, radioactivity, infectious substance hazards and environmental hazards. The regulations give standards for the packaging and for any tanks that are used for transport, they also layout a system of communicating the hazards of substances using pling and marking of packages, signage on tanks, freight containers and vehicles, and the documentation and emergency response information that is required to accompany each shipment.

Percentage of formulation statements

In Regulation (EC) 1272/2008 Annex I section 3.1.3.6.2.2 it says:


In the event that an ingredient without any useable information at all is used in a mixture at a concentration of 1 % or greater, it is concluded that the mixture cannot be attributed a definitive acute toxicity estimate. In this situation the mixture shall be classified based on the known ingredients only, with the additional statement that “x percent of the mixture consists of ingredient(s) of unknown toxicity”


also in Annex I section 4.1.3.6.1 it says:


In the event that no useable information on acute (short term) and/or chronic (long term) aquatic hazard is available for one or more relevant components, it is concluded that the mixture cannot be attributed to one or more definitive hazard category(ies). In this situation the mixture shall be classified based on the known components only, with the additional statement in the SDS that: “Contains x % of components with unknown hazards to the aquatic environment”

Hazard and Prevention statements

The R & S phrases have been used within the EU for several years but will be gone after 1^st June 2017, when, any mixtures that are still on the shelf must be relabelled to conform to the CLP regulations. The R phrase is being replaced with the hazard statement and the S phrase is being replaced by the prevention statement, the advantage of the new codes is that they will be used in all countries that implement the UN GHS framework, which will make it easier for businesses to operate internationally.

CLP classifications and categories

Not all of the UN’s classifications have been implemented within the EU and they do not always match the CHIP classes, so some chemicals will appear to be more or less hazardous than they were.

Each classification and category has a signal word (danger, warning or no word), depending on how dangerous the substance is. All classifications and categories have at least one pictogram except for eight that do not and one that has two.

There are lowest concentration percentage trigger points for the classifications & categories, these range upwards from 0.1%. The lowest trigger point value depends on how hazardous the substance is for example Carcinogenic 1A & 1B = 0.1% and Carcinogenic 2 = 1.0%.

The German Water Hazard Regulations

Full translated name is “Regulation on the Classification of Substances hazardous to waters into Water Hazard Classes” (Verwaltungsvorschrift wassergefährdende Stoffe – VwVwS) or abbreviated to either WGK (Wassergefährdungsklassen) or VwVwS.

This regulation came into force originally in November 1996 and has been modified several times since. The regulation sets out that all substances are either non-hazardous to water (ngw, nicht wassergefährdende) or assigned to one of three classes:

                WGK 1: Low hazard to waters

                WGK 2: Hazard to waters

                WGK 3: Severe hazard to waters

When a substance is not named in the regulations it is possible to use the R-phrase classifications for a substance to calculate the WGK classification, it must be kept mind that this always depends on the most sensitive data item.

What is LD50/LC50?

LD50 and LC50 are standard measures for expressing and comparing the toxicity of chemicals, LD50 is the abbreviation for lethal dose 50 and LC50 is the abbreviation for lethal concentration 50, usually in air or water. The value that is associated with either is the lowest amount of the chemical, given in one dose, which is required to kill 50% of the test subjects. Toxicologists can use many kinds of animals but testing is usually done with rats and mice.