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Chemical safety in the laboratory
Introduction
Improper handling of hazardous chemicals can produce significant health and/or physical harm. For many years countries issued their own national regulatory standards to assure employees were informed of the hazards in the workplace. The regulations and descriptions of hazards varied between countries. In 2003 the United Nations established the Globally Harmonized System (GHS) for the classification and labeling of chemicals. This GHS, adopted by the majority of the countries, has established a uniform system throughout the world for identifying chemicals and communicating their hazard information on labels and safety data sheets. Most of this chapter references the GHS ( ). The goal is to help one understand the chemical hazards and properly handle chemical substances in the histology laboratory. Whilst this chapter is written from the perspective of the United States and the appropriate code of federal regulation (CFR) numbers are referred to, it can be readily applied to any country.
Classifications of hazardous chemicals
The United Nations GHS provides detailed criteria to assign the hazard classification to a chemical substance. Each classification is also assigned a category number. The category number indicates the severity of the hazard: Category 1 represents the greatest hazard risk; higher numbers have lower risk factor. Classifications are divided into three major groups ( Table 2.1 ). The GHS assigns to each classification standardized text/symbols which includes hazard statements, a signal word, a pictogram ( Table 2.2 ), and precautionary statements.
Table 2.1
GHS hazard classifications
| Health hazards | Physical hazards | Environmental hazards |
|---|---|---|
| Acute toxicity | Explosives | Acute aquatic toxicity |
| Skin corrosion/irritation | Flammable gases | Chronic aquatic toxicity |
| Serious eye damage/eye irritation | Flammable aerosols | |
| Sensitization | Oxidizing gases | |
| Germ cell mutagenicity | Gases under pressure | |
| Carcinogenicity | Flammable liquids | |
| Reproductive toxicity | Flammable solids | |
| Specific target organ system toxicity-single exposure | Self-reactive substances | |
| Specific target organ system toxicity-repeated exposure | Pyrophoric liquids | |
| Aspiration toxicity | Pyrophoric solids | |
| Self-heating substances | ||
| Substances which in contact with water emit flammable gases | ||
| Oxidizing liquids | ||
| Oxidizing solids | ||
| Organic peroxides | ||
| Substances corrosive to metal |
Table 2.2
GHS hazard classifications and assigned pictogram (29 CFR 1910.1200 appendix C )
| Flame over circle | Flame | Exploding bomb |
|---|---|---|
|
|
|
| Corrosion | Skull and crossbones | Gas cylinder |
|---|---|---|
|
|
|
| Health hazard | Exclamation mark | Environment |
|---|---|---|
|
|
|
A chemical can have multiple hazard classifications assigned. For example, the common clearing agent, xylene, is classified with multiple physical and health hazards. Table 2.3 shows the GHS information assigned to xylene ( ).
Table 2.3
GHS classification and information for xylene
| Hazard classification | Flammable liquids, Category 3 Acute toxicity-dermal, Category 4 Acute toxicity-inhalation (vapors), Category 4 Skin irritation, Category 2 Serious eye damage/eye irritation, Category 2 Carcinogenicity, Category 2 Specific target organ toxicity-single exposure, Category 3 Specific target organ toxicity-repeated exposure, Category 2 Aspiration toxicity, Category 1 |
| Signal word | Danger |
| Pictograms |    |
| Hazard statement | Flammable liquid and vapor Harmful in contact with skin Causes skin irritation Causes serious eye irritation May cause respiratory irritation May cause drowsiness or dizziness Suspected of causing cancer May be harmful if swallowed and enters airways May cause damage to organs through prolonged or repeated exposure |
| Precautionary statements | Prevention, response, storage and disposal statements |
Labeling of hazardous chemicals
In the USA, the Occupational Safety and Health Administration’s (OSHA) Hazard Communication (29 CFR 1910.1200) requires the following elements to be placed on labels of hazardous chemicals:
- 1.
Product name
- 2.
Signal word (Danger or Warning)
- 3.
GHS Hazard statement (classification)
- 4.
GHS Pictograms
- 5.
GHS Precautionary statements
- 6.
Name, address and telephone number of the chemical manufacturer
Chemical manufacturers use the standardized GHS tests to classify a chemical and label it accordingly. If a laboratory mixes its own reagents, they would need to follow the same GHS criteria to determine the hazard classification of the reagent in order to label it correctly. This would be time consuming and/or expensive.
For laboratory prepared reagents, searching the internet for a manufactured equivalent reagent can provide the GHS classifications. Lot numbers, date of preparation (manufacturing), and person who prepared the reagent are other pieces of information that can be added to labels as required by a facility’s protocols. In the USA, chemicals which are manufactured and labeled in compliance with other regulatory agencies are exempt from the GHS label format (29 CFR1910.1200(b)(5)).
Exempted chemicals include beverage alcohols, drugs, medical devices, pesticides, tobacco products and cosmetics. In the pathology laboratory, fixatives, processing reagents and stains are considered medical devices and are thus exempt from the GHS labeling.
Working safely with hazardous chemicals
Whenever possible, hazardous chemicals should be replaced with safer alternatives, or volume usage should be reduced. Mercury is an example of a hazardous material which has been banned in many U.S. hospitals; thermometers and sphygmomanometers are now using mercury replacements. Pathology laboratories in turn have replaced the mercury-based fixatives (B-5, Zenkers) with zinc-based fixatives.
It may not be possible to eliminate all hazards from a laboratory but the risk factor can at least be reduced. Formaldehyde is classified as a carcinogen. Formaldehyde-free fixatives using glyoxal have equivalent preservation characteristics without the carcinogenic properties of formaldehyde ( ). Similarly, the clearing agent xylene requires solubility criteria for tissue processing and staining. The various xylene substitutes (aliphatic hydrocarbons, limonene) provide the solubility criteria without the physical flammability hazard of xylene or the high multiple health hazards.
Safety data sheets (SDS)
Formerly known as Material Safety Data Sheets (MSDS), SDS are the primary source for identifying the hazards and proper handling requirements of a chemical. Prior to GHS there were multiple MSDS formats being used. Without a standardized format it was difficult to find information, especially during an emergency. The GHS established a standardized 16 section SDS format ( Table 2.4 ). Sections 1-8 provide general information and also any information which may be needed quickly in an emergency (e.g. first-aid, spill, fire). Sections 9-12 have scientific data on which the classification is based and Sections 13-15 have regulatory information. Manufacturers are required to send SDS with the initial shipment of a chemical and whenever a change has been made in the SDS (29 CFR1910.1200(g)). Training programs should constantly be updated to assure dissemination of any new SDS information.
Table 2.4
GHS safety data sheets format
Section 1: Identification of the substance or mixture and of the supplier
This section provides the name of the product and must match the name found on the label. The section may list other common chemical names. For example, formaldehyde gas is also known as methanal, methylene oxide and methyl aldehyde. The Chemical Abstract Service # (CAS#) is a unique numerical code issued by the American Chemical Society to identify a chemical; the chemical formula may also be provided in Section 1 . The EC# is also a chemical identifier for chemicals marketed in the European Union (EU). Some suppliers list the catalog number to make tracking and reordering easier. The recommended use of the chemical will also be provided. Generally, the latter will be generic with such listing as ‘laboratory chemical’. The supplier’s contact information and an emergency telephone number are also provided. When an emergency telephone number is identified as CHEMTREC or CHEMTEL, that number is only to be used for a transportation emergency response and not for a medical emergency or a laboratory spill cleanup.
Section 2: Hazards identification
This section will provide the classification(s) of the chemical. In addition, all the label’s elements will be found in this section of the SDS (signal word, pictogram(s), hazard statements, precautionary statements).
Section 3: Composition and information on ingredients
The chemical name as well as the common name will be listed for all components which contribute to the chemical hazard. Any hazardous impurities or stabilizers will also be included. An example of a hazardous stabilizer is found in 37% formaldehyde. Formaldehyde will polymerize to form solid paraformaldehyde and methanol, between 7-14%, is added to the aqueous solution to inhibit this reaction. Therefore, methanol, a hazardous chemical, is listed in the SDS as part of the composition of 37% formaldehyde. Besides the name, CAS#, EC# and concentration/concentration ranges are listed. A statement is required from the manufacturer when the specific chemical identity and/or exact percentage of composition has been withheld as a trade secret (29 CFR1910.1200(i)(1)).
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