Chemicals are hazardous for many reasons. The categories of hazardous chemicals are detailed below:
Any chemical used in a laboratory should be handled with care and according to laboratory procedures. Prior to performing work involving chemicals, safe handling procedures and the chemical's Materials Safety Data Sheets (MSDS) must be reviewed. If mixing chemicals, the reactivity of each must be reviewed to avoid adverse chemical reactions.
While a wide range of chemicals and processes are used in various laboratories, the following sections detail the general safety practices that must be followed:
** Chemical reactivity worksheet (from U. S. National Office of Response and Restoration). Download is available for interactive reactivity worksheet.
Many chemicals used in laboratories may be toxic. Toxicity depends on the quantity, frequency and duration of exposure, or the dose. Toxic effects can be local (at the site of exposure) or systemic (at another site in the body), acute or chronic. When dealing with toxic chemicals, it is important to consider the route of exposure and the target organ to ensure that proper controls are adhered to.
When planning and conducting experiments, it is critical to recognize that the combination of toxic effects of two or more substances may be significantly greater than that of one substance alone. Toxic reaction products can be much more dangerous than the starting reagents. Many cases of toxic reaction products occur when chemicals are mixed unintentionally. This can occur due to improper labelling, mishandling of chemicals and spills.
Laboratory workers must be able to recognize the potential hazards present to prevent exposure to toxic chemicals, and in the event of accidental exposure, know the procedures for emergency, spill response and first aid.
All substances are poisons; there is none which is not a poison. The right dose differentiates a poison... (Paracelsus).
The single most important factor that determines whether a substance is harmful is the relationship between the amount/concentration and the toxic effect it produces. This is referred to as the dose-response relationship. Many chemicals are toxic with one small exposure, while others require repeated doses (chronic exposure). It is important to remember that this relationship is unique to each chemical.
The toxicity of a chemical is best identified by its lethal dose 50 (LD50). LD50 is defined as the amount of a chemical that when given to a specified laboratory animal (e.g. rat), it will kill 50% of the animals. The LD50 is usually expressed in mg/kg or g/kg of body weight. Thus, chemicals with low LD50's are highly toxic, requiring a low dose to cause fatal effects. For chemicals where the hazard is inhalation, the LC50 (lethal concentration 50), which is the concentration of chemical in air, is more often used. LC50 is usually expressed in ppm, mg/L or mg/m3. This information is found on the MSDS.
Acute and chronic effects
The duration and frequency of exposure are factors in whether a chemical will produce a toxic effect. While effects can occur after a single dose (acute), or with intermittent (repeated), or long-term (chronic) exposures, the specific chemical and route of entry determine the effect. Some chemicals are acutely toxic, while others require repeated exposures or have long-latency effects (effect appears long after the exposure).
Generally, the longer the duration and/or frequency of exposure, the greater the toxic effect. For certain chemicals, the body is able to eliminate the toxins and/or repair tissues to some degree, thus the time between exposures will also affect the total dose required for a response.
Routes of exposure
Ingestion - Refers to exposure by entrance through the mouth and swallowing. The substance enters the gastrointestinal tract and is absorbed into the system through the blood stream. Ingestion is a method of exposure that is highly preventable through use of proper personal protection equipment, personal hygiene practices and adherence to rules regarding eating, drinking and use of cosmetics in the lab.
Inhalation - Gases, vapours, aerosols, particulates, fibers and dusts can enter the body and cause either local or systemic effects by absorption through the mucous membranes in the mouth, throat and lungs.
For gases, the most important factor in rate of absorption is solubility. Chemicals that are highly soluble easily penetrate the lung tissue and blood, which allows them to be transported to other organs. For solids, particle size determines where a particle can penetrate and how far into the respiratory tract it can travel. Solubility of the particle (fat or water-soluble) also determines whether it will be cleared from the body, or remain for long periods of time causing chronic or long-latency disease.
A major factor in inhalation is the vapour pressure of the chemical - the higher the vapour pressure, the greater the potential of it being released into the air. It is also important to remember that vapour pressure increases with temperature, therefore by heating a substance, the likelihood that hazardous vapours will be produced increases. Procedures to control the production or release of airborne toxins are important to prevent both acute and chronic exposures. Ventilation through the use of fume hoods is the key control measure in preventing inhalation exposure. It is also necessary to reduce the surface area of solvents exposed, to cover containers, and to follow procedures to avoid spills.
Absorption - Can occur through intact or broken skin, or via a body orifice (e.g. eye, ear). Either the skin itself may be injured, or the chemical may be absorbed into the body and transported via the bloodstream. Use of PPE such as lab coats, gloves and goggles are the best method of protection against absorption.
Injection - Needles, razor blades, broken glass or other sharp objects that pierce the skin can allow toxic chemicals or biohazardous agents to enter the body. Proper handling and disposal of sharps is necessary to eliminate this method of exposure.
Use and storage of flammable liquids
Flammable liquids can be easily ignited, even at concentrations less than their lower flammable limits, and at temperatures below their flash point. Vapours may be heavier than air, thus allowing them to travel long distances along the ground where they may reach an ignition source.
Part IV (s.4.12) of the Ontario Fire Code governs quantities of flammable liquids that are handled or stored in Laboratories. All laboratories must conform to these requirements.
Section 126.96.36.199(1) of the Ontario Fire code states:
The container size used for the storage of flammable or combustible liquids in a laboratory shall be not more than 5 L capacity.
Classification of flammable liquids
|Description||Class||Boiling point (°C)||Flash point (°C)|
|Flammable||IA||< 37.8||< 22.8|
|Flammable||IB||> 37.8||< 22.8|
|Flammable||IC||---||> 22.8 and < 37.8|
|Flammable||II||---||> 37.8 and < 60|
|Combustible||IIIA||---||> 60 and < 93.3|
Part IV of the Ontario Fire Code restricts dispensing flammable or combustible liquids from containers of more than 5 L capacity. Dispensing flammable or combustible liquids from containers of 5 L capacity or less is permissible in laboratories at University of Waterloo (UW) provided the dispensing is performed in an approved chemical (fume) hood. Chemistry Stores (ESC 109) is the only location on campus that has been designed and approved to dispense flammable or combustible liquids from containers with greater than 5 L capacity.
Flammable/combustible liquids in the open lab
A maximum of 300 L of combustible (class II and III) and flammable liquids (class I), of which no more than 50 L can be flammable (class I), can be outside of a flammable liquid storage cabinet at any one time.
Flammable liquids storage cabinets
A maximum of 500 L of combustible (class II and III) and flammable liquids (class I), of which no more than 250 L can be flammable (class I), can be stored in an approved flammable liquid storage cabinet. Each lab is permitted a maximum of 3 flammable liquid storage cabinets.
Flammable liquid storage cabinets conditions of use
- For storage of flammable liquids only (no acids, bases, oxidizers, etc.)
- Bungs must be in place, covering flame arresters
- This cabinet may only be ventilated after approval by Plant Operations
- Individual containers must be:
- Maximum 5 L capacity
- Clearly labelled
- Tightly closed
Location of work for flammable or combustible liquids
All work, research, investigations, etc. involving flammable or combustible liquids must be carried out in an approved chemical (fume) hood when:
- Their use releases flammable vapours which could be potentially explosive
- Liquids are heated to a temperature greater than their flash point
- Unstable liquids are used
Where refrigerators are required to keep flammable liquids (class I) at a controlled temperature the refrigerator must:
- Be approved by the Electrical Safety Authority
- Be identified as containing flammable liquids
- Have all containers within the refrigerator tightly closed
Oxidizing agents represent a significant hazard in the laboratory due to their capacity to undergo violent reactions when they come into contact with reducing agents, causing ignition in flammable and combustible materials. Oxidizers can also increase the intensity of a small fire, making safe storage a key consideration in the lab. In addition to the risk of fire, oxidizers may release toxic gases either by reacting with other chemicals, or through decomposition caused by heating. Oxidizers on their own can also have corrosive properties.
Oxidizers may be found in both solid and liquid form. Solid oxidizing agents such as metallic chlorates, perchlorates, nitrates, chromates and permanganates may form explosive mixtures with oxidizable dusts and other suspended particles (e.g. flour, coal dust, magnesium powder, zinc dust, carbon powder).
Liquid oxidizers include nitric acid, chromic acid and sulphuric acid. In addition to being oxidizers, these are also corrosive chemicals. One of the most hazardous liquid oxidizers is perchloric acid, and should be avoided if possible. If perchloric acid must be used, workers must be trained in safe handling procedures and a perchloric acid fume hood designed and constructed for this purpose must be used.
Although inorganic peroxides can be hazardous, they are generally stable. However, they may generate peroxides in the presence of organic compounds, or can react violently in the presence of water. More hazardous are organic peroxides, which will be discussed in detail below.
Organic peroxides are carbon-based chemicals that contain the characteristic peroxide (-O-O-) bond. Many organic peroxides are shock, heat, or friction sensitive. The inadvertent production or concentration of organic peroxides have been the cause of many well-documented accidents. Safe handling and storage procedures for hazardous chemicals must be followed when dealing with organic peroxides.
Peroxide formers are compounds that may react with oxygen, even in low concentrations and temperatures often not considered as hazardous. Peroxidation is a hazard affecting primarily liquid peroxide formers, and solids that are finely divided.
The risk of peroxide formation exists when the compound is exposed to oxygen. This occurs when containers are not properly sealed. Peroxidation occurs more rapidly at elevated temperature and pressure. Blanketing peroxide formers with an inert gas reduces the opportunity for oxygen to reach the compound during storage. Become familiar with the known peroxide formers and classes in the tables below.
Follow these precautions for storing and handling peroxide formers:
- Label all known and suspected peroxide formers. Date containers upon receipt and after testing for peroxides.
- Store peroxide formers blanketed with an inert gas, such as nitrogen or argon.
- Store in original containers or in amber-coloured glass bottles with plastic caps. Containers must be well-sealed, away from sources of light.
- Dispense quantities as needed. Do not return unused material to stock container.
- Store at cool temperatures, however do not refrigerate. Refrigerating or freezing may cause peroxides to precipitate out.
- Peroxidizable chemicals must be dated when received. If the material is kept longer than the recommended storage time the material must be tested for peroxides, and the test date and results attached to the container. If the peroxide content exceeds 100 ppm the material must be disposed of or the peroxides neutralized.
- If possible, add an oxidation inhibitor to increase the safe storage life of peroxide forming organic chemicals. Inhibitors are depleted over time and must be replenished periodically.
- Avoid friction, grinding and any form of impact during handling or transport. Do not use glass containers with metal screw caps or glass stoppers.
- Never use a metal spatula, use ceramic or plastic instead.
- Follow lab procedures for personal protective equipment and hygiene. Avoid ingestion, inhalation or skin contact.
- Procedures which result in evaporation of peroxide formers or extensive exposure to air or oxygen are should be avoided. Distillation of any peroxide former should not be attempted unless the material has been tested for the presence of peroxide. Uninhibited Class C chemicals should not be distilled.
Moieties that may form Peroxides
|Ethers and acetals with alpha hydrogen|
|Alkenes with alyllic hydrogen|
|Fluoro or chloroalkenes|
|Alkylalkyenes with alpha hydrogen|
Classes of peroxide formers
|Class A||Class B||Class c|
|Definition||Chemicals that form explosive levels of peroxides without concentration||Chemicals that form explosive levels of peroxides on concentration||Chemicals that may autopolymerize as result of peroxide accumulation|
|Maximum storage||3 months||12 months||
Uninhibited chemicals - 24
Inhibited chemicals - 12 months
Diethylene glycol dimethyl ether Dioxanes
Ethylene glycol dimethyl ether 4-Heptanol
Methyl isobutyl ketone
Other secondary alcohols
- a - When stored as a liquid monomer
- b - although these chemicals form peroxides, no explosion involving these monomers has been reported
- c - when stored in liquid form, these chemicals form explosive levels of peroxides without concentration. They may also be stored as gas in a cylinder. When stored as a gas, these chemicals may autopolymerize as a result of peroxide accumulation.
Kelly, Richard J. . U.S. Department of Energy, Lawrence Livermore National Laboratory.
American Chemical Society. Safety in Academic Chemistry Laboratories.
Corrosive materials include chemicals that will result in an immediate, acute erosive effect on tissue as well as other materials. Corrosive chemicals include strong acids and bases, dehydrating and oxidizing agents, and halogen gases.
When handling corrosive chemicals, the eyes and skin are most commonly at risk, however failure to use proper protective equipment and handling procedures can result in exposures to the respiratory and digestive tract through inhalation and ingestion as well.
Corrosive chemicals exist in solid, liquid and gaseous forms. Some examples and their effects are:
Corrosive solids - Sodium hydroxide, phosphorous, phenol. Dust from these can be inhaled and cause serious damage to the respiratory tract.
Corrosive liquids - Bromine, sulfuric acid, aqueous sodium hydroxide, hydrogen peroxide. The danger in liquid form is the speed at which the liquid reacts upon contact, causing immediate destruction of tissue.
Corrosive gases - Chlorine, ammonia, nitrogen dioxide, hydrogen chloride, formaldehyde. Exposure occurs through inhalation, causing damage to the lining of the respiratory tract and lungs.
Special consideration must be given to the use of hydroflouric acid or hydrogen flouride. It should be avoided if at all possible, and if used, workers must be trained in safety procedures, first aid, and spill response. Specific procedures for hydrogen flouride are below.
Hydrogen fluoride standard
Hydrofluoric acid is highly corrosive and toxic even in a dilute form, therefore any contact with skin or eyes must be treated as a medical emergency. The following procedures will assist the user in the safe handling of hydrofluoric acid. Further information is available from the Safety Office.
Personal protective equipment
The following equipment is to be used when handling hydrofluoric acid:
- Eye and face protection as appropriate (approved splash goggle and full face shield)
- A splash apron
- Gloves (neoprene or nitrite rubber)
- Fume hood (plastic sash window)
Any laboratory possessing hydrofluoric acid must have:
- Hydrofluoric acid burn cream (2.5% Calcium Gluconate in Muko gel) available from Chemistry Stores (ESC 109).
- An approved eye wash and emergency shower.
Skin (large burns)
- Treat as medical emergency-call ambulance immediately-dial 911.
- Rinse affected area until ambulance arrives (protect eyes from contamination and remove contaminated clothing ).
Skin (small burns)
- Rinse affected area for 15 min. with water and then apply burn cream liberally to affected area.
- Get medical aid (Health Services, family physician or hospital).
Eyes (any amount)
- Treat as medical emergency-call ambulance immediately-dial 911.
- Rinse eyes with water until ambulance arrives.
- Treat as medical emergency-call ambulance immediately-dial 911.
- Rinse mouth liberally with water.
- Do not induce vomiting.
- Treat as medical emergency-call ambulance immediately-dial 911.
- Remove victim to fresh air.
- If breathing stops rinse acid from mouth and administer artificial respiration.
When water-reactive chemicals come into contact with water, one or more of the following reactions can occur:
- Release of heat and potential ignition of the chemical or other materials
- Release of flammable, toxic or oxidizing gas
- Release of metal oxide fumes (reactive metals only)
- Formation of acids
These materials must be stored away from any source of water or moisture. Some examples include:
- Alkali metals (lithium, potassium, sodium)
- Aluminum chloride and
- Acetyl chloride
Pyrophoric chemicals will ignite spontaneously upon contact with air due to the extreme rate of oxidation. These must be stored under inert gas or mineral oil or other hydrocarbon liquids. Metals, when finely divided are pyrophoric. Some examples of pyrophoric materials are:
See section on organic peroxides under oxidizers.
An explosive is any chemical compound or mechanical mixture that, when subjected to heat, impact, friction, detonation, or other suitable initiation, undergoes rapid chemical change, evolving large volumes of highly heated gases that exert pressure on the surrounding medium. This term applies to materials that either detonate or deflagrate.
Explosives are regulated by the Canadian Explosives Act and Ontario Fire Code regulations, and any use, handling or storage must conform to these regulations.
Picric acid is a common reagent used mainly in biological laboratories. The hazard related to picric acid is dehydration- when it dries, it becomes a dangerous explosive. In addition, when in contact with metal, picrate salts can be formed, which are highly shock-sensitive. The following safety precautions must be adhered to:
- Picric acid must be stored in water.
- Containers are to be inspected at least every 6 months and distilled water added to the containers as necessary to ensure that dehydration does not occur.
- Never use metal containers or lids to store picric acid. Metal spatulas are never to be used.
- Always wipe the neck and cap of the bottle before returning to storage.
**If dehydrated picric acid is discovered, contact the Safety Office at ext. 36268 for disposal.
Provide safe handling procedures for ethidium bromide
Potential hazards (please consult your MSDS)
- Consult the Material Safety Data Sheet on ethidium bromide before using the chemical.
- Wear personal protective equipment when handling ethidium bromide.
- Lab coat
- Nitrile gloves
- Closed toe shoes
- Splash Goggles
- Eye wash/deluge shower
- Leave personal protective equipment in laboratory.
- Work with ethidium bromide in a designated area.
- Equipment used with ethidium bromide should be designated as such and not used for other work unless decontaminated.
- A UV light may be used to detect the presents of ethidium bromide, remember to use appropriate protective equipment when using UV lights.
- Before using any chemical, participate in Workplace Hazardous Materials Information System (WHMIS) training, be familiar with the properties and hazards of the chemicals by reading the Materials Safety Data Sheet (MSDS), which describe boiling point, flash point, vapour pressure, toxicity, explosive limits, incompatibilities, and other special precautions.
- Use proper caution at all times when handling chemicals as many (whether solid, liquid or gaseous) are poisonous to the human body to some degree.
- Handle chemicals which may release vapours in fume hoods in such a manner that the vapour will be removed. Vapours create most of the dangers in the laboratory. They may be toxic, flammable, or both.
- Keep hands away from face, eyes, and body until after hands have been washed thoroughly when handling chemicals.
- Flush skin with plenty of fresh water if a chemical is splashed or spilled on skin. Report the incident to your lab supervisor.
- Use a eye wash station if a chemical enters the eye immediately for a minimum of 15 minutes or according to the MSDS.
- Never test chemicals by taste or smell.
- Pour chemical waste solutions into containers specified by your lab supervisor.
- Do not store incompatible chemicals in proximity to each other. See specific chemical storage guidelines.
- Do not use unlabeled chemicals.
- Mixing of chemicals must be done under controlled conditions, following an approved process and safety procedures. Prior approval must be obtained, and a safety report is required if the work has not been done by the individual worker before.
- Chemicals stored in glass bottles must be placed in secondary containers that are made of non breakable material when they are transported from one location to another.The
- Primary rule for handling acids is to add acid to water, never the reverse. This is to avoid splashing of acid onto skin or into eyes when heat is generated upon mixing.
Safe chemical storage is extremely important in maintaining a safe lab and preventing injury, fire, explosion and spills.
General chemical storage guidelines
- Read the MSDS to determine how the chemical should be stored. Ensure that MSDS for all chemicals being used are readily available.
- Ensure that all containers are labelled and in good condition. Date chemicals when they are purchased, especially peroxide formers.
- Segregate incompatible chemicals according to guidelines below.
- Storage areas must be dry and well ventilated.
- Do not store chemicals near heat sources or in direct sunlight.
- Minimum quantities of hazardous chemicals should be stored. Dispose of chemicals that are no longer required.
- Flammables must be stored in approved flammable liquid storage cabinets, or in approved explosion-proof refrigerators.
- Secure gas cylinders away from heat sources and according to UWaterloo's cryogenic and compressed gas safety program.
- Never store chemicals on the floor.
- Chemical storage shelves should have a raised lip to prevent containers from falling. Secondary containers or bins should be used to limit spills should they occur.
- Shelves should not be overloaded, and must be secured against tipping.
- Never store liquid or corrosive chemicals above eye-level.
- Chemical containers should be checked on a regular basis for leakage.
- All containers must have tightly sealed caps when not in use.
- Store chemicals close to work areas to minimize transport distance. When transporting glass containers, use secondary containment receptacles to minimize breakage and spillage if the container is dropped.
- Prevent access to storage areas of unauthorized persons.
- Do NOT store chemicals in fume hoods. This will reduce the effectiveness of the hood and increase the risk of spills and interaction of incompatible chemicals.
Specific chemical storage guidelines
|Water reactive chemicals||
|Non-volatile, non-reactive solids||
Follow these procedures for biological, chemical and radioactive materials.
Prior to work with hazardous materials
- Determine spill procedures from MSDS for all chemicals.
- All UW employees and students handling hazardous materials are required to be trained in spill procedures.
- Obtain proper spill kits and clean up equipment. Available from Chemistry Stores ESC 109.
Small spill that poses no immediate threat to health
- Notify occupants in the immediate area of the spill.
- Use spill kits to absorb and contain according to spill procedure.
- Place material in a secure and ventilated area.
- Contact Safety Office at ext. 35755 for disposal instructions.
Large spills or spills that pose an immediate threat to health
- Remove sources of ignition if possible.
- Evacuate immediate area.
- Call UWaterloo police ext. 519-888-4911 or ext. 22222.
Contact UWaterloo Safety Office ext. 35755 with any questions or for assistance.
All chemical, biological and radioactive wastes are to be disposed of at the environmental safety facility located on the first floor of Earth Sciences and Chemistry (ESC) Rm. 150 . Material may be delivered to the facility Monday to Friday from 11:00 A.M. to 12:00 Noon or a pickup may be arranged by calling ext. 35755.
University policy requires compliance with environmental regulations.
Do not put any hazardous materials in the regular garbage or into the drains.