Chemical safety

"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.

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.

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.

• 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

All work, research, investigations, etc. involving flammable or combustible liquids must be carried out in an approved chemical (fume) hood when:

1. Their use releases flammable vapours which could be potentially explosive
2. Liquids are heated to a temperature greater than their flash point
3. Unstable liquids are used

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 4.12.3.1(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.

Where refrigerators are required to keep flammable liquids (class I) at a controlled temperature the refrigerator must:

1. Be approved by the Electrical Safety Authority
2. Be identified as containing flammable liquids
3. Have all containers within the refrigerator tightly closed

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.

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:

1. Eye and face protection as appropriate (approved splash goggle and full face shield)
2. A splash apron
3. Gloves (neoprene or nitrite rubber)
4. Fume hood (plastic sash window)

First aid

Any laboratory possessing hydrofluoric acid must have:

1. Hydrofluoric acid burn cream (2.5% Calcium Gluconate in Muko gel) available from Chemistry Stores (ESC 109).
2. An approved eye wash and emergency shower.

Skin (large burns)

1. Treat as medical emergency-call ambulance immediately-dial 911.
2. Rinse affected area until ambulance arrives (protect eyes from contamination and remove contaminated clothing).

Skin (small burns)

1. Rinse affected area for 15 min. with water and then apply burn cream liberally to affected area.
2. Get medical aid (Health Services, family physician or hospital).

Eyes (any amount)

1. Treat as medical emergency-call ambulance immediately-dial 911.
2. Rinse eyes with water until ambulance arrives.

Ingestion

1. Treat as medical emergency-call ambulance immediately-dial 911.
2. Rinse mouth liberally with water.
3. Do not induce vomiting.

Inhalation

1. Treat as medical emergency-call ambulance immediately-dial 911.
2. Remove victim to fresh air.
3. If breathing stops rinse acid from mouth and administer artificial respiration.

Resources

Hydrogen Fluoride Protocol

Safety Office Recomendations for Hydrofluoric Acid Spill Station

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)
• Silanes
• Magnesium
• Phosphorous
• Aluminum chloride and
• Acetyl chloride

Aqua regia (hydrochloric acid/nitric acid mixture) and piranha (sulfuric acid/hydrogen peroxide) solutions are both highly aggressive (corrosive) acids as well as being strong oxidizers. On top of this aqua regia is a solution that continually breaks down (off-gasses) to form fumes of nitrogen peroxide. Both solutions must be prepared in quantities for immediate use only and then disposed of immediately when the work is done. As the solutions are unstable, they should not be prepared and stored for future use and should never be stored in a sealed container, especially a glass one. When preparing and using the solution, it should be done in an open top beaker in a fume hood to allow for off-gassing.  Please be aware that there is a large amount of heat (exothermic) generated in the making of these solutions so appropriate PPE must be worn (gloves/goggles/face shield/apron) and ensure there is an eye face wash/drench hose or an eyewash/shower combination available within 10 seconds of travel, and pathway free of obstructions that may inhibit the use of equipment. For disposal of these solutions, they should be diluted by adding the solution slowly to water (dilute by at least 10 times the original quantity, 20 times is recommended) and then neutralized using sodium bicarbonate or a solution of sodium hydroxide to a pH of 5. At this point, the solution can be safely poured down the drain with copious amounts of water, unless there are any hazardous materials still in solution (ie. heavy metals). For further information, contact the Safety Office at ext. 35755.

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:

• Manganese
• Phosphorous
• Chromium
• Nickel
• Titanium
• Iron
• Calcium
• Cobalt
• Boron
• Cadmium
• Phosphine

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.