RECOGNIZING LABORATORY
HAZARDS: PHYSICAL HAZARDS
PHA297-Laboratory safetyCORROSIVE HAZARDS
Corrosives are defined as chemicals that cause harm or injury by damaging and destroying tissue, such as eyes or skin, at the point of contact or the exposure site.
Most common corrosives are some acids, bases, oxidizing agents and gases.
Minimizing exposure is very important. Proper precautions should be used.
Corrosive Chemicals that May Be Encountered in Faculty of Pharmacy Labs
Acids Bases Oxidizing Agents Gases
Hydrochloric
acid Sodium hydroxide Hydrogen peroxide Ammonia Sulfuric acid Ammonium
hydroxide Potassium permanganate
Nitric acid Nitric acid
Acetic acid
CORROSIVES - ACIDS
The potential for injury by an acid depends on its chemical structure, the area of the exposure, the concentration of the solution, the duration of exposure, and the temperature of the solution. The greater the concentration, duration, and temperature encountered, the greater is the potential for harm.
HCl, H2SO4, HNO3
Strong acids (and strong bases) in concentrations greater than 1 molar are usually corrosive. While concentrated and dilute may just sound like relative terms to describe the molarity of solutions, in acid–base chemistry these have specific definitions. Concentrated means that the acid or base has the molarity of saturated solutions. Dilute is a less well-defined term and means that the
concentration is lower than concentrated. This could be 6 M, 1 M, or less. So, while a “dilute
solution” may sound like a “safe” one, 6 M is still pretty concentrated and probably quite hazardous.
Acids generally cause damage to proteins, forming a substance called coagulum. As this substance accumulates it can block or prevent further damage to underlying tissues. This is why acids may be less damaging than bases, but nevertheless all corrosives have the potential to be very damaging.
When diluting an acid, you should always pour acid into water. While the reverse process, pouring water into acid, may sound like an equivalent procedure, it is not.
CORROSIVES - ACIDS
Since acetic acid is a weak acid (Ka = 1.7 × 10−5) and you probably know it also as the principal component of vinegar, it may seem to be a reasonably safe compound. In low concentrations it is.
However, acetic acid is sometimes used in its “glacial” form that is 99.8% acetic acid. Not only is acetic acid at concentrations >50% flammable (which is not a common danger associated with most acids), glacial acetic acid has a very high affinity for water and is a strong dehydrating agent. The
exothermicity of this reaction is sufficient to cause burns. Vapors of glacial acetic acid are understandably quite dangerous if inhaled.
Phosphoric acid is a weak acid (Ka1 = 7 × 10−3) but can also be found in pure, 100% form. Phosphoric acid is also known as ortho-phosphoric acid and it solidifies below 21 ◦C. It is hygroscopic and a strong corrosive. In high concentrations it can cause severe burns to the skin. At lower concentrations it is an irritant. While phosphoric acid as a mist can be irritating to the eyes, nose, throat, and respiratory
system, it is unlikely to cause pulmonary edema.
While all acids are very hazardous in concentrated form, hydrofluoric acid (HF) is extremely hazardous, and HF solutions ≥0.01 molar concentrations are very corrosive. While you are not likely to encounter HF in your early laboratory sessions, you should know something of its especially hazardous nature and that it requires special treatment upon exposure. HF solutions must be handled with great care, and exposures to HF require special attention with flushing for only 5 minutes rather than the normal 15
minutes, then immediate, specific medical treatment, typically with benzalkonium chloride (Zephiran) or calcium gluconate. No work should be done with HF unless these pharmaceuticals for treating HF burns are present, are readily available to the laboratory or to a nearby medical clinic or hospital, and a plan has been made with medical staff to treat these HF burns in the event of an exposure.
CORROSIVES - BASES
NaOH (caustic soda), KOH (caustic potash) - highly corrosive
They are mostly in pellet form and both liquid and solid forms are extremely corrosive and exposure can cause severe burns.
Dissolving these hydroxide pellets in water generates a lot of heat, and a hot corrosive can be even more hazardous. If you have some of these pellets in the palm of your hand, they will quickly absorb moisture from your hand and/or the air and can generate a very concentrated (saturated) solution.
Ammonium hydroxide, another base commonly used in the laboratory, is a weaker base than the alkali bases, but at high concentrations is also highly corrosive and irritating to the skin, eyes, and mucous membranes.
Additionally, ammonia gas is released from ammonia hydroxide solutions and this ammonia can be very irritating to the eyes and mucous
membranes
.CORROSIVES - BASES
In general, bases can cause severe damage because exposures may not be immediately painful, but harmful reactions with body tissues begin immediately if they are not removed immediately from the
skin or point of contact. Bases act in a different way than do acids. Hydroxide ions saponify (break up) fats and proteins, and the bases continue to penetrate deeper into the skin or site of exposure, causing
damage unless they are consumed or thoroughly washed away. We previously discussed how acids initially damage tissue, but the damaged tissue eventually forms a protective layer that prevents further
damage. However, damage by bases does not form protective layers, so corrosive action continues until
the base is washed away or used up. Furthermore, bases are not easily removed and it takes continuous
washing for some time to remove them. The key here is to prevent exposure, but if you are exposed, you must take action quickly to avoid tissue damage.
NaOH
EYE EXPOSURE
The eye is especially susceptible to severe damage from exposure to corrosives. The concentration and length of exposure determine the amount of damage or injury. The eye is resistant to changes from solutions in the range of pH 3–10; however, outside this pH range (<pH 3 or >pH 10), the eye’s epithelium is rapidly destroyed.
Eye exposure to concentrated sulfuric acid can be extremely serious due to the affinity of sulfate ions for corneal tissue, its dehydrating effect, and its high heat of hydration.
Reducing exposure time is critical to prevent permanent damage or blindness—every second is important. Any exposure of base or acid should immediately be treated with thorough washing with water for at least 15 minutes, followed by an immediate
examination by a physician in a nearby clinic or hospital emergency room.
