Laboratory Safety Manual - Chapter 06: Safe Handling of Chemicals

Title

Laboratory Safety Manual - Chapter 06: Safe Handling of Chemicals

Purpose

This chapter discusses the major routes of exposure to chemical substances during laboratory work, and several safe handling practices that can minimize your risk while working with chemical substances. The last section lists practices for the safe use of hydrofluoric acid.

Table of Contents

1. Introduction
2. Routes of Exposure
   1. Dermal Contact
   2. Inhalation
   3. Ingestion
   4. Injection
   5. Ocular Exposure
3. Safe Handling Practices for Toxic Materials
   1. Access Control
   2. Personal Practices
   3. Decontamination of Work Surfaces
   4. Minimizing Aerosols
   5. Use of Laboratory Hoods and Biological Safety Cabinets
4. Specific Handling Procedures for Hydrofluoric Acid
   1. Hazards - Overview
   2. Dermal Exposure Case Studies
   3. Handling and Personal Protective Equipment
   4. Post-Exposure Treatment
   5. Incompatibles and Storage
   6. Spills

I. Introduction

All chemicals can have toxic effects at some dose level and particular route(s) of exposure. It is therefore wise to minimize exposure to chemicals. Chemicals can have local or systemic effects. Local toxicity refers to the direct action of chemicals at the point of contact. Systemic toxicity occurs when the chemical agent is absorbed into the bloodstream and distributed throughout the body, affecting one or more organs. Health effects can be acute or chronic. Acute effects last for a relatively short time and then disappear. Chronic effects are not reversible.

Do not confuse acute and chronic exposure with acute and chronic effects. Acute exposures to chemicals are for short periods. Chronic health effects can develop from acute exposures depending on the properties and amount of the chemical. Acute or chronic adverse health effects can also occur with chronic (repeated) exposure to chemicals, even at low concentrations.

II. Routes of Exposure

A. Dermal Contact

Skin contact is one of the most common chemical exposure routes in laboratory settings. Spills and splashes can result in overt skin contamination. In addition, laboratory personnel may unknowingly contaminate themselves when they touch work surfaces, glassware, or equipment contaminated during experiments. A common result of skin contact is localized irritation or dermatitis. However, a number of materials are absorbed through the skin to produce systemic poisoning. The main portals of entry for chemicals through the skin are the hair follicles, sebaceous glands, sweat glands, and cuts or abrasions of the outer layers of the skin. The follicles and the glands contain blood vessels, which facilitate the absorption of chemicals into the body. Chemicals can also enter the body when contaminated hands touch the mouth, nose, eyes, sores or cuts. For more information, refer to the glove use policy in Chapter 5: Protective Clothing and Equipment.

B. Inhalation

Inhalation of toxic vapors, mists, gases, or dusts can produce poisoning by absorption through the mucous membrane of the mouth, throat and lungs, and can seriously damage these tissues by local action. Inhaled gases or vapors may pass rapidly through the capillaries of the lungs and enter the circulatory system. The degree of injury from inhalation of toxic substances depends on the material’s toxicity, solubility in tissue fluids, concentration, and the duration of exposure.

Although inhalation hazards are more often associated with gases and volatile chemicals, both solids and non-volatile liquids can also present an inhalation hazard for laboratory personnel. Laboratory chemicals in the form of dusts and particulates can become airborne when transferred from one container to another. Grinding and crushing procedures can also produce aerosols. Splashes created from spills and vigorous shaking and mixing form aerosols. Many of these generated particulates do not settle out but remain suspended in the air and travel along air currents in the room. Some of these particulates can be inhaled and deposited in the respiratory tract. For many operations, you might not recognize that aerosols are present and a hazardous situation exists. All laboratory operations involving an open vessel will result in aerosol release. Such operations include weighing, stirring, pouring, pipetting, injections with a needle and syringe, handling animals, and removing caps and stoppers. As an alert laboratory person, take care not to create aerosols.

C. Ingestion

Ingestion of toxic materials in the laboratory can occur when contaminated hands come in contact with the mouth, or with food items. The laboratory environment can contaminate food items and utensils. Do not mouth pipette, as this can result in aspiration of toxic materials. For more information, refer to the laboratory food policy in Chapter 3: General Safety Principles and Practices.

D. Injection

Accidents involving needles and syringes can result in injection of toxic and/or infectious materials through the skin. Needles and syringes are among the most hazardous items used in the laboratory, especially when combined with the task of inoculating an uncooperative animal. Containers of toxic chemicals may break, resulting in hazard from contact with contaminated broken glass.

E. Ocular exposure

The eyes are of particular concern, due to their sensitivity to irritants. Ocular exposure can occur via splash, or rubbing eyes with contaminated hands. Few substances are innocuous with eye contact, and several can cause burns and loss of vision. The eyes have many blood vessels, and rapidly absorb many chemicals. For more information, refer to the eye protection policy in Chapter 5.

III. Safe Handling Practices for Chemical Substances

A. Access Control

The Principal Investigator must control access to laboratories that contain chemicals. Keep the laboratory door closed while experiments are in progress. This practice not only protects persons who might otherwise enter the laboratory, but it reduces interruptions to laboratory staff that could lead to accidents. Laboratory hoods offer the most worker protection, when the doors to the laboratory are closed.

B. Personal Practices

Wash your hands immediately after completion of any procedure involving chemicals, and when leaving the laboratory. Soap must be either liquid or foam in a pump dispenser. Do not use bar soap in laboratories. Do not use liquid soap bottles that you must invert and squeeze. Soap dispensers can be wall-mounted type or freestanding countertop bottles.

Figure 6.1
Wall-mounted and freestanding liquid and foam soap pump dispensers are appropriate for laboratory use.
Invert-squeeze soap bottles and bar soaps are not acceptable for laboratory use.

In laboratories where toxic materials are used, do not eat, drink, smoke, chew gum, apply cosmetics, or store utensils, food, and food containers, unless your laboratory has an authorized and clearly marked food item area. Refer to the food policy in Chapter 3. In some laboratories, it might not be possible to establish a food item area due to the lack of adequate containment of volatile or toxic substances. If your laboratory has a food item area, make sure no chemicals, procedures, or laboratory equipment end up in the area. Remove gloves or other personal protective equipment that could introduce contamination to the food item area. Consider posting a reminder or labeling equipment.

Figure 6.2 - Improper use of food item areas.
(Left): Do not handle chemicals, or wear contaminated gloves, in a food item area.
(Right): Do not place laboratory equipment (such as this water bath) within three feet of a designated food item area.

Use mechanical pipetting aids for all pipetting procedures. NEVER MOUTH PIPETTE.

C. Decontamination of Work Surfaces

Protect work surfaces from contamination by using “bench paper” (disposable plastic-backed absorbent paper) or stainless-steel trays. Place the plastic side down and the absorbent side facing up. Change worn or contaminated bench paper and dispose of properly. Decontaminate other items and equipment with appropriate solvents when contaminated during experiments.

D. Minimizing Aerosols

Since a procedure with an open vessel of liquids or powders generates aerosols, you should develop techniques that will minimize the creation of aerosols. Such techniques might include discharging liquids from pipettes as close as possible to the fluid level of the receiving vessel, or allowing the contents to run down the wall of the receiving vessel. Dropping the contents from a height generates more aerosols.

Also, avoid rapid mixing of liquids with pipettes by alternate suction and expulsion, or forcibly expelling material from a pipette. Take extra care when discarding contaminated gloves or plastic-backed absorbent paper used to cover the work surface, to avoid aerosolizing contaminants. Clean floors with a wet mop or with a vacuum cleaner equipped with a HEPA filter, as dry sweeping or dry mopping contaminated laboratory floors could aerosolize contamination.

E. Use of Chemical Fume Hoods and Biological Safety Cabinets

When used properly, chemical fume hoods and biological safety cabinets are among the most effective means for controlling exposures to toxic chemicals, since they move substances away from you before they can reach your breathing zone. Refer to Chapter 16: Biological Safety Cabinets and Chapter 17: Chemical Fume Hoods for a full discussion of the uses and limitations of these very important engineering controls.

IV. Specific Handling Procedures for Hydrofluoric Acid

A. Hazards - Overview

Hydrofluoric acid (HF) differs from other acids because it readily penetrates the skin and dissociates into fluoride ions, causing destruction of deep tissue layers, including bone. The fluoride ion affects tissue integrity and metabolism by liquefaction necrosis, decalcification and destruction of bone, and production of insoluble salts. Loss of calcium (hypocalcemia) results from precipitation of calcium from the blood as CaF₂. This results in calcium loss from the bones to equilibrate the decreased serum calcium. The development of hypocalcemia can be rapidly fatal because calcium is important for muscles, including the cardiac muscle (heart), to function properly. Fluoride ions might also bind to potassium and magnesium ions, leading to myocardial irritability and arrhythmia. Death from metabolic acidosis, hypocalcemia, or ventricular arrhythmias can occur several hours after exposure.

Pain associated with skin exposure to HF may not occur for 1-24 hours. Unless you can rapidly neutralize the HF and bind the fluoride ions, tissue destruction may continue for days and result in limb loss or death. HF is similar to other acids in that the initial extent of burn depends on the concentration, temperature, and duration of contact with the acid. Eye exposure to concentrations of HF greater than 0.5% can result in severe ocular damage, with delayed signs and symptoms.

Hydrofluoric acid vapors are also hazardous. Ocular irritation and injury can occur from working with HF outside a vented enclosure (laboratory hood). Inhalation can cause severe throat irritation, cough, dyspnea, cyanosis, lung injury and pulmonary edema. In severe exposure cases, these can result in death.

B. Dermal Exposure Case Studies

• An adult patient who developed 25% total body surface area second degree burns after exposure to a 70% hydrofluoric acid preparation died in cardiac arrest. Ionized serum calcium level was 1.7 milligrams per deciliter (mg/dL) immediately premortem. The normal range is 4 to 4.8 mg/dL.
• A dermal exposure to 70% hydrofluoric acid over a 2.5% total body surface area resulted in death. The serum calcium level was 2.2 mg/dL.
• Two workers died following a splash exposure of 70% hydrofluoric acid to the face, chest, arms and legs. Both workers were promptly removed from site of exposure. Clothing was removed and burns were initially treated at the workplace with a cold shower and alcohol applied to burn areas. No suitable protective clothing was worn at the workplace.
• A woman died from severe chemical burns of the skin and lungs, with intense pulmonary hemorrhagic edema after having acid thrown onto her face during an attack.
• A patient with HF burns over 8% of his body died from intractable cardiac arrhythmia secondary to the depletion of ionized calcium.

C. Handling and Personal Protective Equipment

• Familiarize yourself with the hazards specific to HF before handling. Consult this Chapter, the SDS, the EHS HF webpage and label information.
• Always handle HF in a properly functioning laboratory hood, and in an area equipped with an eyewash and safety shower.
• Do not work alone when using HF and alert colleagues when using the material.
• Ensure that non-expired calcium gluconate antidote is on hand before handling HF.
• Required Personal Protective Equipment:
  • Goggles
  • Face shield (plastic)
  • Gloves: Thin disposable gloves (such as 4, 6, or 8 mil blue nitrile gloves) used in laboratory operations provide a contact barrier only and should be disposed immediately when contamination is suspected. Thicker (10-20 mil) PVC or neoprene gloves provide better resistance to HF but do not provide the necessary dexterity for many lab procedures. Thinner PVC or poly gloves can provide some resistance to HF, but require immediate changing at the first sign of contamination. Do not wear disposable gloves without double gloving because of the potential for exposure through pinholes
  • Acid resistant apron
  • Long pants and sleeves (note that these are required when working with all corrosive materials, including HF)
  • Closed toe shoes (required for ALL laboratory work)

D. Post-Exposure Treatment

This manual (Chapter 3, Section VIII) contains a recommendation that upon skin or eye exposure to hazardous materials, flush the affected area for at least 15 minutes with an eyewash or safety shower. This general guidance is appropriate for almost every lab chemical, including corrosive acids and bases. However, HF has more specific treatment requirements, outlined below.

Figure 6.3 - Tube of calcium gluconate gel. Make sure you have one or more non-expired tube of this present in your lab when working with HF.

In the event of a skin or eye exposure to HF:

• Have someone call 911 immediately, to facilitate arrival of medical assistance.
• Remove all exposed clothing and immediately wash all exposed areas with copious amounts of water from the safety shower or eyewash. Flush exposed eyes for at least 15 minutes, but flush exposed skin for only five minutes, followed by treatment with a calcium source.
• For skin exposures, after flushing for five minutes, apply a gel or slurry of calcium gluconate (preferred) directly to the exposed area. Use concentrations between 2.5% and 33%.
• For severe exposure cases, consider subcutaneous infiltration with calcium gluconate. Infiltrate each square centimeter of affected dermis and subcutaneous tissue with about 0.5 mL of 10% calcium gluconate, using a 30-gauge needle. Repeat as needed to control pain. Split or remove nails to treat nail bed burns. The earlier this is administered, the more rapidly symptoms resolve.
• CAUTION: Avoid administering large volumes of subcutaneous calcium gluconate, as this will result in decreased tissue perfusion and potential necrosis.

Note that calcium gluconate gel has an expiration date. Make sure that you always have access to a non-expired supply if you are working with HF.

DO NOT USE CALCIUM CHLORIDE - Calcium chloride is irritating to the tissues and may cause injury.

Incompatibilities and Storage

Figure 6.4 - Hydrofluoric acid. Note that the storage bottles are plastic. Make sure to store all forms of HF, including dilutions and waste, in compatible containers that are not glass.

Store HF and HF waste in a cool, dry place away from incompatible materials. Storage areas should be clearly marked as containing HF. HF reacts with many materials; therefore, avoid contact with glass, concrete, metals, water, other acids, oxidizers, reducers, alkalis, combustibles, organics and ceramics. Store in containers made of polyethylene or fluorocarbon plastic, lead, or platinum. Place storage bottles in polyethylene secondary containment trays.

Never store HF, or HF waste, in glass containers.

Spills

Ensure all areas where HF is used are equipped with proper spill response equipment. You can neutralize small spills (100 mL or less) by covering with magnesium sulfate (dry) and absorbing with spill control pads or other absorbent materials. Add sodium bicarbonate or magnesium oxide to any absorbent and place in a plastic container for disposal. Wash the spill site with a sodium bicarbonate solution.

Use 3M’s Universal Sorbent or similar, as it does not react with HF. Do not use spill sorbents that contain silicon, such as vermiculite or sand, as this can produce silicon tetrafluoride, an odorless toxic gas.

If the spill is large, in a confined space, or in an area where there is not adequate ventilation, evacuate the room and immediately report the spill to 911. Contact EHS at 919-962-5507 if you have questions about spill response, or if you do not feel comfortable trying to clean up the spill yourself.

Back to Chapter Five

Proceed to Chapter Seven