CHEMICAL LABORATORY SAFETY INTRODUCTION TO LABORATORY SAFETY

Objectives

Introduction to Laboratory Safety introduces the hazardous properties of chemicals and defines term commonly used to describe them:

• toxicity

• corrosivity

• flammability

• reactivity

and lists sources of information about these chemicals.

TOXICITY

Toxicity is the adverse effect a substance has on a biological system.

TOXINS AND POISONS

Toxins and poisons are those substances which exhibit toxicity.

Pathways of Toxins into the Body

• Inhalation

• Absorption

• Ingestion

• Injection

Some Effects of Toxins

• Headaches

• Narcosis

• Dizziness

• Liver damage

• Cancer

• Death

Exposure

Exposure is determined by

DOSE (amount of toxin)

DURATION (length of time)

Local Toxicity

Local toxicity occurs at the site of exposure (example: rash)

Systemic Toxicity

Systemic toxicity occurs at a particular organ or site remote from exposure.

Target Organs

Systemic toxins usually have effects concentrated in particular target organs:

• benzene: blood forming process (leukemia)

• phenol: nervous system

• chlorinated hydrocarbons: liver and kidneys

Allergic

Allergic reactions are caused by an acquired sensitivity to a chemical.

Additional Systemic Toxins

• teratogens: developmental defects in a fetus

• mutagens: changes in DNA

• carcinogens: cause cancer

Toxic Effects are also classified as:

Acute: immediate with single or short term exposure

Chronic: delayed reaction after repeated or prolonged exposure

Latency Period

The latency period is the delay between exposure and when the effects of exposure appear.

THRESHOLD LIMIT VALUES (TLV)

The human body processes defense mechanisms against most, if not all, types of toxins. However, there is a limit to these defense mechanisms, and these limits vary from person to person. Therefore, we express the limits as the maximum allowable exposures for most people.

(Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices - ACGIH)

PERMISSIBLE EXPOSURE LIMITS (PEL)

Similar to TLV except these are part of the OSHA (Occupational Safety and Health Administration) database for permissible limits of exposure.

Three Types of Exposure Limits

• TWA - 8 hour time weighted average (chronic)

• STEL - short term exposure limits (acute)

• CL - ceiling limits (acute)

Time Weighted Average (TWA)

The TWA is the limit on the average concentration of a chemical to which an employee is exposed during an 8 hour workday. Each chemical will have its own TWA.

Short Term Exposure Limits (STEL)

Some substances, mostly acute toxins, have short term exposure limits designed to limit exposure for a period shorter than 8 hours. A 15 minute interval is commonly used.

The STEL is higher than the TWA if a chemical has both.

Ceiling Limits (CL)

Some toxins are controlled with a ceiling limit. This limits exposure over an "instantaneously" short period of time. Exposure to a chemical must never exceed this limit for any period, no matter how short.

CORROSIVITY

Corrosive chemicals cause visible destruction of, or irreversible alterations in, living tissue by chemical action at the site of exposure.

Corrosive chemicals are typically acids and bases. There are no set quantitative regulations governing skin or eye exposure for these chemicals. PEL and TLV do set limits for inhalation of the vapours or mists.

To protect against skin and eye contact, isolate the operation as much as possible by using fume hood sashes and shields.

Always wear eye protection and other personal protective equipment as appropriate for the operation (gloves, lab coat, face shield).

flammability

A flammable is a substance whose vapours will ignite when exposed to an ignition source at temperatures below 100 degrees fahrenheit (37.8 centigrade).

COMBUSTIBLE

A substance which must be heated above 100 degrees Fahrenheit in order to be ignited.

FLASH POINT

The minimum temperature at which vapours from a substance will ignite and substain a flame. This temperature is referred to as the flash point (FP).

Classifications of Flammable and Combustible Liquids

Flammable liquids are divided into three classes (IA, IB, IC) based on flash points and boiling points.

Combustible liquids are divided into three classes (II, IIIA, IIIB) based on flash points.

Classes of Flammable and Combustible Liquids

To comply with OSHA regulations, the employer must be aware of the class of each flammable liquid used. These classes determine the type of container and container size.

The laboratory facility and type of fire protection must take these classes into account.

The following table lists the maximum allowable container sizes for each class of flammable or combustible liquid.

Under OSHA regulations, one-gallon containers are permitted if:

• the liquid would be rendered unfit by contact with metal or would corrode.

• single assay lots of one gallon are necessary for experimental purpose.

OSHA regulations permit up to 25 gallons of flammable liquids in a single fire area. (29 CFR 1910.106)

The National Fire Protection Association bases the amount on the type of building and fire protection equipment. (NFPA 45)

There are also local and state codes which might even be more stringent but make sure these limitations are used because they are designed for your safety.

The Fire Triangle

Three elements are necessary for ignition:

• fuel

• an oxidizer (usually air)

• a source of ignition (energy)

If any of the 3 are eliminated, ignition is not possible.

The fuel can be eliminated by substitution of nonflammable ones or proper storage techniques.

Because of air, the oxidizer is more difficult to eliminate. In some cases a technique called inerting can be used.

Be aware that there are other oxidizers which include halogens, nitrates, nitrites, and chlorates.

Control of Ignition Sources

Ignition sources are normally the easiest to eliminate.

Common sources are electrical switches and thermostats, electric motors, control devices, telephones, and static electricity.

Isolate these from places that may contain fuel-air or spills of flammable liquids - either by distance or special devices (enclosures or pressurization).

Ignition sources should be kept off the floor because vapours from flammable liquids are denser than air and will collect at low points.

Vacuum pumps used on the floor should be modified to be "explosion proof".

Refrigerators used to store flammable materials must be designed for that purpose. These special refrigerators have no sources of ignition on the inside (light bulbs or thermostat contacts).

The "explosion proof" ones even have their motors and compressors isolated to prevent ignition and control ignition if it occurs.

Electrical devices can be placed under positive pressure or an inert gas to keep them away from flammable vapours.

To prevent static electricity, maintain the relative humidity above 40%.

Flammable liquids can build up a static charge just by the action of sloshing around in a container during transport.

When transferring flammable liquids from one container to another, always ground any metal. Ensure that good electrical contact is made, and any painted coatings are penetrated to the base metal.

Autoignition

When a heated substance ignites spontaneously without an external ignition source.

The temperature at which this occurs is called the autoignition temperature.

Flammable Range

In order for combustion to be self-sustaining, the ratio of fuel to air must be within certain limits.

• Lower explosive limit (LEL)

• Upper explosive limit (UEL)

REACTIVITY

Reactivity is the hazard from chemicals or combinations of chemicals that react violently or explosively releasing a large amount of energy. Sometimes reactive chemicals can create additional hazards such as the evolution of toxic or flammable vapours.

Self-Reactive Chemicals

Self-reactive chemicals are substances which have unstable molecular structures and can release energy violently on their own without reacting with another chemical.

Heat or shock are the most common ways self-reactive chemicals are accidentally initiated.

In most cases, using a solvent reduces the risk by separating reactive molecules.

Air and Water Reactivity

Some chemicals will react exothermically with water.

Pyrophoric - ignite spontaneously when exposed to air (ie white phosphorus)

Water reactive chemicals are of special concern due to firefighting procedures.

Delayed Reactions

Delayed reactions are caused by the induction period before the rate of reaction increases.