PROCEDURES FOR ACIDS AND BASES
Acids and bases are corrosive and will destroy body tissue. The extent of injury depends on factors such as the type and concentration of the chemical, the route of exposure, the type of tissue contacted, and the speed used in applying emergency measures. Acids, especially in concentrated form, are most likely to cause immediate pain upon contact with tissues. High concentrations of hydrofluoric acid will cause immediate pain and tissue destruction. These effects may be delayed by several hours with weaker concentrations. Fluoride ion from hydrofluoric acid also penetrates the deep tissue layers and can cause bone damage. Skin contact with strong bases usually goes unnoticed, since pain does not occur immediately.
The eyes are especially susceptible to acids and bases and must be immediately flushed with water for at least 15 minutes if exposure occurs. Inhalating acid fumes and airborne dust and mist from bases irritate the nose, throat, and lungs. Pulmonary edema, a severe irritation of the lungs resulting in fluid production that prevents the transfer of oxygen to the bloodstream, can also occur from intense extreme airborne exposures. Secondary toxic effects may occur if the material is absorbed from the lungs into the bloodstream. The extent of these effects depends on the concentration in air and the duration of exposure. Ingestion causes severe burns of the mucous membranes of the mouth, throat, esophagus, and stomach.
Dilution of acids and bases is exothermic. This is particularly true for sulfuric acid and potassium hydroxide. Concentrated solutions of inorganic acids and bases are not in themselves flammable. Combustion can occur, however, when an oxidizing acid is mixed with other chemicals or with combustible materials. Acids also react with many metals, resulting in the liberation of hydrogen, a highly flammable gas. Bases such as sodium hydroxide will liberate hydrogen gas upon reaction with aluminum, magnesium, tin, and zinc metal. Some acids are strong oxidizing agents and can react destructively and violently when they come in contact with organic or other oxidizable materials. Perchloric acid may form explosive perchlorate crystals, which are shock-sensitive and can detonate. Acids can form toxic reaction products when combined with cyanide or sulfide salts. The corresponding products are hydrogen cyanide and hydrogen sulfide gas.
- Work Leads are responsible for identifying acids and bases used in the work area. Review sources such as MSDSs for specific compounds.
- An assessment of the hazards and controls in place is necessary to limit employee exposures to these agents. Contact an EH&S Industrial Hygienist to provide assistance. This is especially important for hydrofluoric and perchloric acids, aqua regia, and piranha etch.
- Some operations involving acids and bases may require an AHD. This is determined by the using Division in accordance with the provisions in PUB-3000, Chapter 6, “Safe Work Authorizations.”
Training and Information
- Employees who either handle or who may be exposed to the hazards of acids and bases are required to complete Chemical Hygiene and Safety Training, EHS 348 (or EHS 345 for Facilities personnel or 352 for summer students).
- All employees in the work area should be trained in the specific hazards and controls of these materials. Area-specific training is a line management responsibility. EH&S Industrial Hygienists are available to provide assistance.
- Consult the section entitled: Labels, for labeling requirements for primary and secondary containers.
- The area entrance must be posted with a Caution Placard depicting the hazards, to convey hazard and emergency contact information.
Substitution and Chemical Inventory Management
- Identify and use safer chemical alternatives if possible.
- If a safer chemical can’t be used, limit what you buy or borrow what you need from a colleague in your group or contact the Chemical Management System coordinator to assist you in finding a source of the chemical at LBNL.
- Conduct periodic cleanouts to prevent accumulation of unneccesary chemicals.
- Procure and use the minimum amount of material required for the operation, or
- Keep working quantities of chemicals to a minimum. Don’t stockpile chemicals.
- Enter these materials into the Chemical Management System (CMS).
- A fume hood or other appropriate exhaust ventilation must be used when handling acids and bases in a manner that may produce an airborne hazard (such as fumes, gases, vapors, and mists). This includes procedures such as transfer operations, preparation of mixtures, blending, sonification, spraying, and heating.
- Operations involving heating or evaporating perchloric acid must be evaluated by an EH&S Industrial Hygienist to determine if special controls (such as using an acid fume hood with wash-down systems to prevent the accumulation of explosive perchlorate crystals) are needed.
- Transfer containers of acid and base solutions in bottle carriers.
- Do not pour water into acid. Slowly add the acid to the water and stir.
- Never empty carboys or drums of chemicals by means of air pressure. Use a tilting rack, a safety siphon, or a liquid pump.
- Use a mechanical aid or a pipette bulb for pipetting.
- Open bottles or carboys slowly and carefully, and wear protective equipment to guard hands, face, and body from splashes, vapors, gases, and fumes.
- Wipe drips from containers and bench tops. Be especially careful to wipe up visible residues of sodium hydroxide and potassium hydroxide from all surfaces. Skin contact with dry residue will result in burns.
- Do not eat, drink, smoke, chew gum, apply cosmetics, or store food, beverages, and tobacco products in work areas where acids and bases are being used.
Personal Protective Equipment (PPE)
Skin and eye contact shall be prevented. The following PPE should be worn when handling these materials. Additional information may be found in the Personal Protective Equipment Section:
- At a minimum, safety glasses with side shields, laboratory coats (coveralls are acceptable in shop settings) and closed-toe shoes will be worn when handling these materials. This is to be considered as minimum protection and must be upgraded if necessary.
- Additional PPE such as chemical goggles, face shields, chemical aprons, disposable coveralls, chemically resistant gloves, and respiratory protection must be worn if there is a greater chance of chemical exposure. An EH&S Industrial Hygienist may be contacted for assistance in selecting appropriate gloves and respiratory protection. The use of respiratory protection requires an industrial hygiene hazard evaluation and a medical clearance followed by a fit test and training by the Industrial Hygiene Group.
- Consult “Eye and Face Protection” in the Personal Protective Equipment Section for guidance on the selection, uses, and limitations of safety glasses, chemical goggles, and face shields.
- The primary concern with acids and bases is chemical burns. However, since many chemicals are skin-absorbers (i.e., agents that readily pass through the skin) it is important to select gloves that are chemically resistant to the material. Consult the PPE section. This contains a list of skin-absorbing agents and provides detailed guidance for selecting chemically resistant gloves.
- Gloves must be selected on the basis of their chemical resistance to the material(s) being handled, their suitability for the procedures being conducted, and their resistance to wear as well as temperature extremes. Improper selection may degrade the gloves, allow the chemical to permeate the gloves and ultimately expose the wearer to the chemical. This is a potentially serious situation. Consult “Gloves” in the Personal Protective Equipment Section for guidance on the selection, uses, limitations, and disposal of chemically resistant gloves. An EH&S Industrial Hygienist may also be contacted for assistance in selecting appropriate gloves.
- Note Regarding Chemically Resistant Gloves for Hydrofluoric Acid: Although Best 8005 NDex Plus nitrile gloves are provided with the HF Exposure Kit (discussed below) and are suitable for applying calcium gluconate gel once the acid has been flushed from the skin, these may not be the appropriate gloves for handling hydrofluoric acid during laboratory operations, as they offer limited chemical resistance under heavy exposure conditions. In selecting the appropriate gloves for hydrofluoric acid, as with all chemicals, the following considerations must be made: the gloves’ chemical resistance to the material(s) being handled, their suitability for the procedures being conducted, and their resistance to wear as well as temperature extremes. Consult the section on “Gloves” for further information and glove selection. The Web link to the ChemRest Guide to Chemical Resistant Best Gloves in this section lists a number of alternatives to the Best 8005 NDex Plus nitrile gloves.
Consult the section entitled Storage Guidelines for hazardous material storage requirements, recommendations and information on chemical incompatibility. Additional requirements are provided below.
- Segregate acids from bases.
- Segregate acids from reactive metals such as sodium, potassium, and magnesium.
- Segregate oxidizing acids from organic acids, and flammable and combustible materials.
- Segregate acids from chemicals that could generate toxic or flammable gases upon contact, such as sodium cyanide, iron sulfide and calcium carbide.
- Store inorganic acids in corrosive or acid storage cabinets. Their interiors and hardware (door hinges and shelf brackets) are corrosion resistant. Corrosive storage cabinets can be located under fume hoods or exist as stand-alone units. Flammable storage cabinets are not corrosion resistant and shall not be used for acid storage.
- Store acids and bases in sealed, air-impermeable containers with tight-fitting caps as opposed to loose-fitting lids or glass stoppers. An exception to this is mixtures that may produce gases that can pressurize the container. These include piranha etch and aqua regia. Piranha etch is a mixture of 98% sulfuric acid and 30% hydrogen peroxide in ratios ranging from 2-4:1. It produces gaseous oxygen. Aqua regia is a 1:3 mixture of concentrated nitric and hydrochloric acids. It produces nitrogen dioxide, chlorine and nitrosyl chloride gases. Either mix fresh batches and use on the same day, or fit containers with vented caps to prevent over-pressurization.
- Keep piranha etch and aqua regia in fume hoods at all times. Note: Normally hazardous materials kept in fume hoods should be limited to those that are in use or that are needed for an activity. But because piranha etch and aqua regia may off-gas these should be kept in a fume hood.
- Do not store aqueous sodium and potassium hydroxide solutions in aluminum drip trays. These will corrode aluminum and compromise its integrity.
- Store nitric and in its own secondary containment trays. Nitric acid can combine with other acids to form nitrogen oxides and nitrosyl halide gases.
- Store combustible organic carboxylic acids such as acetic acid in a flammable storage locker.
- Consult the “Emergency Procedures and Equipment” section for emergency actions regarding chemical spill and personal exposure to chemicals.
- In addition to these requirements, the following applies to acid and base spills:
- Never use combustible or reactive materials (such as paper towels) to clean up or absorb spills. Keep an adequate number of appropriate spill kits to meet anticipated needs:
- Do not clean up or neutralize acid spills with bases (including soda ash, sodium carbonate). In addition, do not neutralize base spills with acids. A potential aggressive and exothermic reaction may ensue. Gaseous carbon dioxide generated from the neutralization reaction can cause splattering.
- Use commercially available acid and base spill cleanup kits that contain “neutralizing agents” and acid/base (pH) indicators. These neutralize spills at a controlled reaction rate, which eliminates splattering and excessive heat generation. The pH indicator provides a visible color change to indicate complete neutralization of the spill. These are available through VWR Scientific.
- It is important to have a sufficient quantity of neutralizer to handle anticipated needs. For example, a JT Baker spill kit contains 3.2 Kg of neutralizing agent. This is sufficient to neutralize the following volumes of the indicated acids:
|Acid and Concentration
||Volume (L) Acid Neutralized by 3.2 Kg of JT Baker Neutrasorb®
|Hydrobromic acid (38%)
|Hydroiodic acid (51%)
|Nitric acid (71%)
|Perchloric acid ((72%)
|Sulfuric acid (98%)
|Sulfurous acid (9%)
The JT Baker Neutracit® caustic spill cleanup kit has 1.2 Kg of neutralizing agent, which has the following neutralizing capacities:
Base and Concentration
|Voume (L) Base Neutralized by 1.2 Kg of JT Baker Neutracit®
|Ammonium hydroxide (28%)
|Potassium hydroxide (45%)
|Sodium hydroxide (50%)
(NOTE: These products can be bought with larger quantities of neutralizing agents.)
- Ensure that you read and understand how to use spill cleanup and neutralizing agents before a spill occurs.
- Add neutralizing agents slowly and deliberately. Understand that a chemical reaction will occur that involves some heat generation and the evolution of gas (normally carbon dioxide).
- Note Regarding Spill Kits for Hydrofluoric Acid: Hydrofluoric acid cannot be cleaned up with normal acid spill kits. Do not use silica-containing agents, especially diatomaceous earth (kitty litter) and sand, to absorb hydrofluoric acid, because they can react with HF to form toxic silicon tetrafluoride gas. Use spill kits such as HF Acid-Eater (NPS Corp) or HF Spill Tamer (JT Baker/Mallinckrodt). HF is a weak acid, and does not completely dissociate. Therefore, sufficient time must be allowed for the neutralizing agent to neutralize the acid.
- An emergency eyewash and safety shower must be located in all areas where acids or bases are used. In the event of skin or eye contact, flush the affected area for at least 15 minutes and report to Health Services for evaluation and treatment.
- Note Regarding Contact with Hydrofluoric Acid and First Aid: Any suspected skin contact with hydrofluoric acid or gas should be treated with flushing as described above, except that flushing should be done for a 5-minute instead of a 15-minute period. Flushing may remove surface hydrofluoric acid, but it does not affect the fluoride ion, which may have penetrated to the deep tissue layers. All work areas where hydrofluoric acid is used must have at least one HF Exposure Kit. These consist of calcium gluconate gel, Best 8005 NDex Plus nitrile gloves for applying the gel, and instructions on what to do in case of exposure. (See the Special Note Regarding Chemically Resistant Gloves for Hydrofluoric Acid, above, regarding the limitations of Best 8005 NDex Plus nitrile gloves for normal laboratory operations). Hydrofluoric acid exposure kits are available through Health Services (ext. 6266). If exposed, flush the affected area for 5 minutes, don the Best 8005 NDex Plus (8 mil thick) nitrile gloves, liberally apply the gel to the affected areas (not the eyes), and report to Health Services immediately.