Science Safety

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Chapter 7

Hazards

Corrosive Chemicals
Reactive Chemicals
Insidious Hazards
Toxic Hazards
Biological Hazards
Radiation Hazards

Corrosive Chemicals

The most familiar corrosive chemicals encountered in laboratories are acids and bases. Corrosive chemicals are substances that are injurious to body tissues or corrosive to metals by direct contact. A corrosive injury may be just a minor irritation or actual physical destruction of body tissue. Corrosive chemicals can be of any phase (gas, liquid, or solid).

What are the hazards?

The action of these substances on body tissues is through

• direct contact with skin
• contact with eyes
• inhalation
• ingestion

The tissues of the body are affected by

• direct chemical reaction
• dissolution of essential components
• destruction of protein
• disruption of cell membranes

Corrosive materials also pose a hazard when dangerous gases are produced as a result of reaction with other materials (e.g., nitric acid will react with copper to produce nitrogen dioxide).

Types of Corrosives and Their Hazards

Perhaps the most important category is the liquid corrosive. Those typically encountered in school laboratories are acids (hydrochloric, sulphuric, nitric, and acetic) and water solutions of bases (sodium hydroxide, potassium hydroxide, and ammonium hydroxide).

Acids act on body proteins causing denaturation and destruction of the protein structure. The denatured protein produces a protein barrier which limits the activity of the acid (although this is extremely painful).

Bases penetrate deeply with little or no pain since no protein barrier is produced. Bases can cause greater skin or eye damage than acids because no protein barrier is produced.

The effects of solid corrosives are related to their solubility in skin moisture, and the duration of contact. Some examples are

• alkali metal carbonates (e.g., Na₂CO₃)
• alkali metal hydroxides (e.g., NaOH)
• alkali metal sulphides (e.g., Na₂S)
• alkaline earth hydroxides (e.g., Ca[OH]₂)
• elemental alkali metals (e.g., Na, K, Li)
• antimony salts*
• arsenic salts*
• chromium salts
• phenol*†
• phosphorus*
• trisodium phosphate

Corrosive solids pose hazards by

• being readily absorbed through the skin (solutions of corrosive solids)
• causing delayed injury (corrosive alkalies may not produce immediately painful reactions)
• being inhaled as dust
• being in a liquid and a molten solid (e.g., phenols*† ) form that greatly increases the threat of exposure

It is a mistake to think of corrosive solids as being relatively harmless because they can be removed more easily than liquids. Solid corrosives are often rapidly dissolved by the moisture in the skin and even more rapidly by moisture in the respiratory and alimentary systems.

Hazards of Phenol*†

Phenol*† is an extremely dangerous solid that must not be present in schools. The hazards posed by phenol include

• being fatal because it is easily absorbed into the system
• producing gangrene from prolonged contact
• affecting
• local areas ­ burns of skin and eyes
• gastrointestinal ­ burns of mouth and larynx, causing nausea and pain
• respiratory ­ breathing difficulties, coughing, cyanosis, and pulmonary edema
• central nervous system ­ headaches, dizziness, visual impairment, convulsions, unconsciousness

Perhaps the most serious hazard associated with corrosives is from corrosive gases. These gases enter the body via absorption through the skin and by inhalation. The corrosive gases are grouped by solubility and effect upon the respiratory system.

Group I	Hazard
ammonia formaldehyde hydrogen chloride hydrogen fluoride* sulfonyl chloride* thionyl chloride*	very soluble, affect upper respiratory tract
Group II	Hazard
arsenic trichloride* bromine* chlorine* iodine phosphorus chloride* sulphur dioxide*	soluble, affect upper respiratory tract and bronchi
Group III	Hazard
carbonyl chloride (phosgene) * nitrogen dioxide* ozone*	least soluble, minimal primary irritation, severe system effects
Group IV	Hazard
acrolein* chlorinated ethers* dimethyl sulphate*	locus of action unknown (toxic activity is not related directly to solubility)

 

The harmful effect of a corrosive gas is not directly related to concentration and exposure duration. To make the problem worse, there are primary effects that can produce severe, immediate damage, and even death without causing systemic injuries. When evaluating possible effects it is necessary to consider the concentration, solubility, and duration of exposure.

Two common corrosive gases are ammonia and phosgene*. Although phosgene is less severe in local immediate effect, it has long-range system effects (pneumonitis).

Corrosive substances may react with another material to give off corrosive, toxic, and flammable gases, and may react to produce other hazardous substances.

Examples

Halogens	They will support combustion, and may ignite powdered metals on contact. Reacts violently with organic substances.
Hydrochloric acid	It can liberate gases such as hydrogen, and hydrogen cyanide. Reacts with formaldehyde to produce chloromethoxychloromethane, a potent carcinogen.
Nitric acid	It can oxidize cellulose material, creating a self igniting condition. Extremely exothermic when mixed with organic materials.
Sulphuric acid	It is a powerful oxidizer that can dehydrate organic material rapidly with the production of heat.
Perchloric acid*	It is a strong oxidant and dehydrating agent. Explodes on contact with many organic substances.

 

Personal Precautionary Measures with Corrosive Chemicals

It is important to

• use adequate protective equipment (safety screen, lab coat, safety goggles/face shield, and gloves)
• use adequate respiratory protection (fume hood, gas mask)
• have adequate exhaust ventilation where corrosive hazards are present
• have plenty of water available for flushing, including eyewash
• have plenty of sodium bicarbonate available for neutralizing liquid corrosive spills
• obtain immediate medical attention upon accidental contact
• store corrosive chemicals properly

Principles of Corrosive Chemical First Aid

• Alert the teacher.
• In the event of contact with eyes, remove contact lenses, then immediately flush the eyes with water and continue to flush for 15 minutes using tempered (not cold) water. Get medical attention if necessary. The first few seconds after contact are critical. Immediate flushing of the eyes may prevent permanent damage. An eyewash fountain is preferred; however, an eyewash hose or any other source of water should be used in an emergency. The only emergency treatment is to dilute the chemical immediately by complete flushing with water. Eyelids may have to be forced open, so that the eyes may be flushed. Alkali (base) burns are usually more serious than acid burns.
• Strong chemicals burn the skin rapidly. There is no time to waste. Begin flushing the area with water immediately. Remove carefully and discard clothing (including socks and shoes), watches, and jewelry. Continue to flood the area, while clothing is being removed.
• Obtain immediate medical attention on accidental contact.
• The precautionary warning on the product label should be consulted for full first-aid information. Provide the label information to the attending physician.
• Neutralizers and solvents (alcohol, etc.) should not be used by the first aider. The spread of a skin absorbable corrosive poison (e.g., phenol*†) can result in death.

Protection

In all cases where a procedure involves a corrosive chemical, wear protective, splash-proof goggles. If corrosive gases or solids are involved, use the fume hood.

Teaching About Corrosive Chemicals

Teachers should demonstrate the safe handling and use of corrosive chemicals whenever applicable, drawing students' attention to correct procedures.

Suggested Teacher Demonstration

Placement:

Senior 1 Science ­ Chemical Interactions
Senior 2 Science ­ Laboratory Safety

Demonstrate properties of acids and bases. Demonstrate dehydrating properties of sulphuric acid on sucrose and relate to effect on body tissues.

Reactive Chemicals

Frequent accidents occur in laboratories simply because the effects of a particular chemical combination have not been anticipated. This is not uncommon even among highly experienced chemists. Refer to Manitoba Regulations 52/88 and 53/88 which are part of the Workplace Safety and Health Act (chapter W120) for specific guidelines for handling reactive chemicals.

The mishandling of reactive chemicals is a well-known problem in science laboratories. Many explosions, fires, burns, and other bodily injuries have been caused by improper and careless handling of reactive chemicals. Misuse does not necessarily refer to problems occurring while the reactive chemicals are being used. It can also result from improper storage, record keeping, and labelling.

The frequency and severity of accidents involving reactive chemicals is minimized by using the data on chemical reactions and incompatible chemicals supplied in this manual, or by reference to specific titles listed in the Bibliography.

Types of Reactive Chemicals

Reactive chemicals can refer to substances which enter into violent reactions to spontaneously generate large quantities of heat, light, gas, or toxicants. Reactive chemicals can be classified as follows:

Explosives are substances that decompose with such speed that they cause a rapid expansion of air, sometimes accompanied by burning gases and flying objects. Some substances are time sensitive in a dangerous manner. Many substances are oxidized by atmospheric oxygen. Ether* and dioxane* may form explosive peroxides after sitting for varying periods (they form green/grey precipitates which are not always noticeable). The containers should not be moved if there is any doubt about stability.

Acid sensitive chemicals react with acids to release heat, hydrogen, explosive gases, and toxicants.

Water sensitive chemicals react with water to release heat and/or flammable or explosive gases.

Oxidation-reduction reactions can occur in any phase, but they tend to generate heat and are often explosive.

Pyrophoric substances burn when exposed to air.

General Precautionary Measures

When dealing with reactive substances, users should

• isolate reactive materials (refer to chapter 6, Chemical Storage)
• ensure that plenty of water is available for flushing where water sensitive substances are not involved
• avoid having water (e.g., extinguishers and sprinklers) in areas where water sensitive chemicals are stored
• store in a well ventilated, cool, dry area, and protect from sunlight
• label properly including the date received and opened, especially in the case of peroxidizable compounds
• protect containers from shock
• keep away from flammables
• wear adequate protective equipment when handling
• order only what is to be used during the year (do not overstock)
• discard old chemicals regularly and properly

An information sheet on reactive chemicals is on page 7.10. Teachers may find it useful to post this sheet in the chemical storeroom.

Reactive Chemicals

Type	Examples	Specific Hazards	Precautionary Steps
Explosives*	Fulminates* Nitroglycerin* Peroxides* (benzoyl, sodium) Picric acid* Azides* Perchlorates (Na, K)* Hydrazines* Dioxane* Ether (not petroleum)*	- Flying objects from explosion - Easily detonated - Can explode from shock, friction, or heat - Unstable - Can form peroxides	Protect from shock, high temperature, sudden temperature changes, and other reactive substances.
Acid Sensitive Substances	Alkali metals Alkaline hydroxides Carbonates Carbides* Nitrides Metals Sulphides Cyanides*	Liberation of heat, flammable gases, and toxicants	Isolate from reactive substances. Wear and use adequate protection.
Water Sensitive Substances	Strong acids and bases Acid anhydrides Alkali metal hydrides Carbides* Aluminum chloride (anhydrous)	- Heat generation - Hydrogen generation - Ignite in moist air, can cause explosions - Can form acetylene or methane - Spontaneously decomposes when stored for long periods and can explode when container is opened.	Isolate from other reactive substances. Store in cool, waterproof area. Wear protective gear.
Oxidation Reduction	Oxidizers Oxygen Mineral acids Perchlorates* Peroxides* (H202 excepted) Nitrites and nitrates Chromates and dichromates Permanganates Halogens Chlorates* Reducers Hydrogen Phosphorous* Alkalai metals Metallic hydrides Formaldehyde	All generate heat and can be explosive	Isolate from each other and other potentially reactive substances. Use adequate protection.
Special Organic Substances	Acrolein* Benzene*	­ Flammable and may also polymerize violently ­ Explodes with many oxidants.	­ Store in an airtight container in a cool place. ­ Isolate from oxidants
Pyrophors	Phosphorous* (white or yellow)	­ Initiation of fire.	Protect from air.

 

Insidious Hazards

Insidious hazards are conditions within the laboratory that represent potential health hazards. These conditions are easily overlooked and ignored because they are not usually conspicuous (seen, tasted, smelled, or felt). They may cause, however, local or systemic, acute or chronic effects, depending upon the nature of the substance and duration of exposure.

In addition, insidious hazards represent a type of problem that users may never be aware of until chronic, systemic poisoning has occurred. All too often insidious or hidden hazards are overlooked during routine safety inspections. Substances such as mercury, present in small droplets on a floor, can emit toxic vapour over a long period of time. Defective safety devices represent another category of insidious hazards.

Explosive perchlorates can form in fume hoods and ventilation systems. Shock sensitive azide salts form in copper drain pipes which are exposed to sodium azide solutions.* Improperly sealed containers of toxic liquids (i.e., carbon tetrachloride* and leaking cylinders of toxic gases) can poison the air.

Mercury Hazards

One of the most common insidious hazards is mercury, both in laboratories and in homes. Mercury is widely used in such such items as electric switches, amalgams, boilers, barometers, thermometers, lamps, and cells. Mercury compounds are also common reagents found on laboratory stock shelves. The hazardous nature of mercury may be overlooked or ignored, even when its hazards are understood because of its widespread use. It may be common practice to aspirate or sweep up any visible drops after an accident involving mercury, but many small droplets may be hidden in small cracks and crevices where they are left to evaporate into the atmosphere.

Characteristics of Mercury

• capable of forming explosive compounds, such as mercury fulminate
• maximum permissible concentration is 0.05 mg/m³ averaged over an 8-hour exposure
• accumulated effect works on the gastrointestinal and central nervous systems
• one mL can increase the mercury level of millions of cubic metres of air to above the permissible concentration

Control of Mercury Hazards

To control mercury requires

• cleaning up immediately and thoroughly after a spill
• storing it in plastic bottles
• storing it under a layer of water or oil
• keeping containers sealed in a cool, well-ventilated area
• providing catch-trays beneath set-ups using mercury
• using care in handling instruments containing mercury
• using gloves
• using a commercial spill kit that includes the control of mercury vapours (aspirator, mercury absorbent, and vapour absorbent)
• using organic-filled thermometers rather than mercury thermometers

Mercury droplets (10-1000 micrometres diameter) stick to vertical surfaces and penetrate into porous flooring. Large amounts of mercury may be left undiscovered after spills. Unless spills are promptly and thoroughly cleaned up and the area decontaminated, the contamination continues.

Other Insidious Hazards

A common source of insidious hazards is the sink drain. If aqueous solutions are disposed of by flushing down the drain, this can lead to the build up of toxic or other hazardous materials that may be released into the laboratory air upon contact with a catalyst (e.g., nickel, metal). Other insidious hazards include

• coal process products
• peroxide formed in old or improperly stored ethers*
• leaking toxic gas cylinders (phosgene*, hydrogen*, cyanide*, and chlorine*)
• mixed chemicals that slowly react to form toxic products or build pressure
• liquid chemicals in glass containers stored above eye level
• explosive perchlorate build-up in fume hoods
• reactive chemicals stored on the same shelf
• faulty pressure control equipment for compressed gases
• ignition sources in flammable solvent areas
• unlabelled chemicals

Control Measures for Insidious Hazards

These measures must include

• preparing an inventory of insidious hazards
• providing adequate ventilation in the form of hoods and forced air as stated in standards and codes
• disallowing stock build-up of toxic, flammable, or corrosive materials
• having efficient and appropriate clean-up agents for spills
• having suitable safety equipment available (e.g., extinguishers and respirators)

Teaching About Insidious Hazards

Teachers should draw students' attention to the presence and control of insidious hazards.

Suggested Lesson Plan:

Placement:

Senior 1 Science ­ Chemical Interactions
Senior 2 Science ­ Elements and the Periodic Table
Senior 3 and 4 Chemistry ­ Safety Introductions

Possible student activities include

• making a poster of instruments that use mercury (Senior 1 Science, during study of the chemical elements)
• researching the use of mercury in industry and how its products are controlled and prevented from entering the environment
• researching mercury poisoning on the body (e.g., Minimata ­ a Japanese toxic chemical disaster)

†Synonyms: carbolic acid, hydroxy benzene, oxybenzene, phenic acid, phenyl hydrate, phenyl hydroxide, phenelic alcohol.

* Must not be present in school laboratories or storerooms.

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