Chemical Safety – General Chemical Safety Guidelines
CHEMICAL SAFETY
All chemicals have some degree of risk attached to their use and it is important before any work is started that a careful investigation is made into the nature and the reaction of the chemicals in use in order to determine whether a hazardous situation could develop. The aim is to protect people against the risks to their health whether immediate or delayed. If the assessment indicates a risk then the hazard must be prevented or controlled and the necessary controls must be properly used and adequately maintained.
COSHH Requirement
No work should be carried out which exposes a person or his/her colleagues to any substance hazardous to health unless a suitable and sufficient assessment of the risks created by that work and of the steps needed to meet the COSHH requirements has been made.
To comply with the COSHH requirements all work must be protected by risk assessment. The risk assessment must be completed by the person carrying out the work and signed by the supervisor who will determine the course of action appropriate to the experiment before work proceeds.
COSHH Assessment Requirements
People carrying out assessment should note the hazards associated with chemicals which can be classified under the general headings:
- 1. Toxicity
- Flammability
- Explosibility
- Biological effect
- Generally offensive
The first step to take when working with chemicals is to find out as much as possible about the concerned chemicals and the possible by-products from published sources. Manufacturers and suppliers have a legal obligation to inform users about the potential hazards associated with the use of their products. In case of new materials where information is not available the judgement must be exercised in predicting whether a material will be hazardous. This may not be always predictable. All personal precautions such as the wearing of gloves, eye protection, and any antidote required should be made available to be ready for use.
Toxic chemicals: It will be advisable to find out if a safer substitute can be used. Personal cleanliness reduces the possibility of ingestion and wearing of personal protective equipment eliminates absorption of the material through the skin. Protective clothing and gloves should always be examined carefully before use, for example, pinholes in gloves can cause serious injury by allowing chemicals to enter the gloves and attacking the skin. All chemicals must be handled inside the extracted wet bench. Any antidotes required should be prepared and made readily available for instant use. Information about the toxicity of chemicals is documented in safety data sheets.
Flammable Materials: These materials should be kept to the minimum quantity, the source of ignition excluded and the correct type of fire extinguisher placed nearby. Materials with a flashpoint below ambient temperature require very careful consideration. The vapour pressure/temperature curve should be carefully examined to check whether an explosive concentration of the substance in the air can develop. All possible sources of ignition should be removed.
Highly Reactive or Explosive Materials: These require very careful handling and reactions involving them should be kept to the smallest possible size. Exothermic reactions should be classified in this category, particular care being taken to ensure that cooling systems do not fail with the result that reaction gets out of control
Generally, Offensive Materials: These produce unpleasant working conditions and frequently the chemicals are toxic too. The best way to minimise unpleasant smell is to handle these chemicals in the extracted wet bench.
Lachrymators and Smokes: These cause intense eye pain and copious flow of tears. Their effects on the eyes and air passages can be serious but the symptoms and pain may disappear after few minutes in the open air. These materials should always be handled in the extracted wet bench. Extra care should be taken when handling substances which may react violently when mixed. This should also be borne in mind when storing chemicals.
Methods of Absorption
There are three main routes by which individuals can be exposed to chemicals:
- Through Skin
- Oral Ingestion
- By inhalation
Through Skin: Certain parts of the skin are more active than others, namely sweat and sebaceous glands, hair follicles, etc. and areas against which clothing rubs are particularly vulnerable. Localised irritation is a most common form of complaint and is enhanced by chemicals which absorb moisture and dehydrate the skin. Corrosive chemicals cause varying degrees of injury from relatively mild attacks to severe burns. Toxic chemicals may be absorbed into the bloodstream after passage through the skin. Eyes are a particularly sensitive area of the body and are irritated by the physical pressure of even the smallest object. When the material is corrosive and toxic pain and injury can be serious.
Oral Ingestion: Oral ingestion of chemicals, apart from the deliberate act, is mainly due to the accidental occurrence and can be easily avoided.
Inhalation: Inhalation is the most common method of absorbing materials into the body. A very large volume of air inhaled by an average person per day means that even the very small amounts of toxic material become important and very large surface area of the lungs increases the chances of the material being absorbed rapidly. Some even may be absorbed into the mucous lining of the air passage and be brought up in the sputum and swallowed, thereby presenting an additional method of absorption.
Symptoms of Exposure
May include Irritation, Burning Sensation, Coughing, Wheezing, Laryngitis, Shortness of Breath, Headache, Nausea and Vomiting.
Acute Effects
Harmful if Swallowed, Inhaled or Absorbed through Skin. Exposure may be extremely destructive to Eyes, Skin, Respiratory Tract and Mucous Membrane.
Exposure may also cause, Nausea, Headache, Vomiting and Convulsions. Inhalation may be fatal as a result of Spasm, Inflammation and Edema of the Larynx and Bronchi, chemical Pneumonitis and Pulmonary Edema.
Chronic Effects
Prolonged exposure can cause:
- Lung irritation, Chest pains, Pulmonary Edema.
- Damage to Blood, Kidneys, Liver, Lungs and Mucous Membranes or irreversible Tissue damage.
- Narcosis of sufficient degree to increase accident prone, impair self-rescue, or materially reduce work efficiency.
- Effect on Central Nervous System.
- Risk of irreversible effects.
Precautions
Almost all hazardous properties of chemicals are largely affected by the size and the and dose and therefore it is necessary, to be aware of the exposure limits commonly called Threshold
Limit Value (TLV). It is a guide considered as being without hazard in a person’s normal working. For a number of chemicals another exposure limit is introduced which is called Short
Term Exposure Limit (STEL) and is defined as the maximal concentration to which a worker can be exposed for a period up to 15 minutes continuously without suffering from Irritation, Chronic or irreversible tissue change or Narcosis of sufficient degree to increase accident proneness, impair self-rescue or materially reduce work efficiency. No more than four periods of this concentration in a day are permitted. Occupational exposure limits (TLV) for chemicals are recorded in safety data sheets. Consult the relevant safety data sheet for guidance. If there is a potential risk then consideration should be given to how the risk can be eliminated or reduced to meet approved standards.
Steps Necessary For Safe Working
- Wear appropriate Protective Clothing, Safety Goggles, Chemical Resistant Gloves.
- Use only in an extracted wet bench.
- Avoid contact with Skin, Eyes or Clothing.
- Do not breath vapour.
- Keep containers tightly closed.
- Wash thoroughly after handling chemicals.
- In case of any mishap seek medical advice as appropriate.
Specific Chemical Hazards
Acetone and Flammable Solvents
Acetone is widely used throughout the facility. It is a very flammable solvent with a low flash point, (i.e. it can be ignited at a low ambient temperature). Because of this, it presents a significant fire hazard. A spill of a gallon bottle of acetone could cause a catastrophic fire or explosion.
It should not be transported except in chemical buckets. Solvents should also be handled with care in the hoods and not used near hot plates. The spilled solvent can be ignited by the hot plates.
The resulting fire could easily be drawn up into the exhaust ducts, again with catastrophic consequences. Spilled solvents can react explosively with chemical oxidising agent present, e.g., peroxides, nitric acid. Spilled solvents should be contained immediately with chemical spillage absorbent. Seek help as required.
Hydrofluoric Acid
Hydrofluoric acid, HF, presents a significant hazard for personal injury. It is widely used in the semiconductor processing. It is only allowed in two designated wet benches, one in staff clean room and other in the chemistry lab. It is available in 40% concentration, diluted, and as the active component of buffered HF, Buffered Oxide Etch. It is used for etching silicon dioxide and for stripping the native oxide prior to further processing.
At the concentrations used in the laboratory, an HF “burn” is initially painless. You may not even know that you have gotten a splatter on your hands, arms, face, or in your gloves. The acid, however, will silently eat away at your flesh. The fluoride ion is not consumed in this process and is soluble in tissue, so the damage penetrates deeper and deeper until it comes to the bone.
About this time the excruciating pain begins. It is too late, however, to reverse the considerable tissue damage. At some point, it enters your bloodstream and goes everywhere scavenging Ca ions, totally messing up the ionic chemistry of your nervous system. At some point, if left untreated, you die. HF burn (courtesy of UC Berkeley) Simple washing of HF splash is not sufficient to prevent damage. It does not wash off; it is already dissolving you and will continue to do so until you receive medical attention specific to HF burns (including deep injections to neutralize the penetrated acid). Be sure that medical personnel know that it is HF burn and know that it requires specific treatment different from a common acid burn.
HF etches silicon dioxide as well as glass. It must not be kept in a glass bottle, used in a glass beaker or disposed of in a glass waste bottle. Plastic laboratory ware is available for this purpose. HF must only be used in the designated extracted wet benches (chemistry laboratory and staff clean room). It is not acceptable to use HF or HF-containing solutions in any other areas.
Piranha Mixture
Liquid piranha is a common name applied to a mixture of Hydrogen Peroxide and Sulfuric Acid (typically 1:5). It is extremely aggressive toward carbonaceous materials (e.g. flesh and photoresist residue, equally).
It also removes heavy metal contamination. It is also used for cleaning Si wafers. We have difficulty disposing of this mixture because the waste continues to react and decompose for a long period of time. This builds up the pressure in the waste bottles causing them burst. Also if the solution is mixed very peroxide rich, one can make unstable compounds.
Therefore, if you wish to use this mixture please make sure you mix only a minimum of the quantities you can live with.
Chlorinated Solvents
Chlorinated solvents (chlorobenzene, trichloroethylene, and methylene chloride) are used in various resist processes. They are particularly bad for you, causing cancer, organ damage, etc. They should not be mixed with normal solvents in waste bottles. There are separate waste bottles for chlorinated solvents. As with most solvents, they can be readily absorbed through the skin.
Glycol Ethers
Commercial photo-resists and electron beam resists are dispersed in a variety of solvents. The composition of these mixtures is generally not disclosed on the bottle; you must look on the MSDS for it. One family of chemicals, the glycol ether, commonly used in photoresists, masquerades under a variety of names. Most photoresists contain one or more of these as solvents. Ethylene glycol mono methyl ether 2-methoxyethanol, Ethyl Cellosolve, 2-ethoxyethanol (2EE), Ethylene glycol mono ethyl ether, Ethylene glycol mono ethyl ether acetate, 2-Ethyoxy ethyl acetate Members of this family of chemicals have been shown to be teratogens and have other effects on reproduction in laboratory animals. A number of recent studies funded by IBM and others have found evidence that these chemicals can lead to miscarriage and other reproductive effects. To quote from the MSDS for AZ 2131 Thinner (2 Ethoxyethyl Acetate and N-Butyl Acetate).
“In studies with laboratory animals, 2-ethoyxethyl acetate caused birth defects, increased foetal death, delayed foetal development, caused blood effects, testicular damage and male infertility.”
The liquid and vapour are eye and respiratory tract irritants and may cause kidney damage, narcosis, and paralysis (in simple terms, it damages your kidneys, eyes, lungs and brains).
Primary routes of exposure are inhalation, skin absorption, and skin and eye contact with vapours. N-butyl Acetate, the other component of this thinner, has a similar list of possible systemic effects.
As with all chemicals, these are only the effects we know about. These experimental laboratory exposures were large amounts but nonetheless, it is prudent to be careful with these solvents. If after reading this section, you still do not have sufficient respect for these chemicals, please go back and read it again. Many users have become sloppy with resist. Don’t be. If you can smell resist in the resist room, somebody is doing something wrong!! Find out what it is and stop it. Users may have resisted on their lab coats or have placed resist-contaminated trash in the wastebasket. This should be avoided.
The conclusion is that you should be careful with the use of even these seemingly innocent chemicals, wear the proper protective equipment and work in a well-ventilated area at all times.
Peroxides
All peroxides are highly oxidizing materials. Considerable energy can be released in their reactions with common materials. Some peroxide compounds are unstable and can explode. containing peroxides. Peroxides are incompatible with all forms of organic solvents and flammable materials.
First Aid Measures
In case of contact rinse affected area immediately with plenty of water while removing contaminated clothing etc. If the inhaled move to fresh air, if there is difficulty in breathing give artificial respiration or oxygen. If swallowed wash out mouth with plenty of water provided the person is conscious. Remove and wash contaminated clothing promptly. Seek medical advice as appropriate.
