Lime
… is a white generally powdery material used in a wide variety of business sectors. But what is lime and what is its danger?
There are different families of lime:
Quicklime :
Quicklime or calcium oxide is a white or greyish granular powder with the chemical formula CaO obtained by calcination (thermal decomposition at about 900°C) of limestone (CaCO3) according to the following scheme: CaCO3 mineral or rock —> CaO solid + CO2 gas
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Quicklime can react violently with strong acids, especially boron trifluoride (BF3) and hydrofluoric acid (HF).
It is possible to react it with water to create slaked lime. The reaction will be as follows: CaO +H2O —> Ca(OH)2 + 1 155 kJ·kg-1CaO
When a large volume of quicklime reacts with water, high heat is released (exothermic reaction). As a result, the water can boil, create lime splashes and cause a thermal burn and/or a chemical burn. In order to reduce the risk of splashing, it is recommended pouring the quicklime gradually into the water (and not the other way around) and to stir the mixture throughout the operation for an even distribution of the heat.
Slaked lime (air lime or hydraulic lime):
Slaked lime or calcium hydroxide is a white or grayish solid with the chemical formula Ca(OH)2 obtained from the reaction of quicklime with water. Slaked lime can decompose into quicklime at a temperature of 580°C.
Slaked lime is a strong base with low water solubility (1.56g/l at 20°C) and the saturated solution has a pH value of 12.4.
Reminder of the pH scale:
- the product is acidic between 0 and 5.5
- it is basic between 9 and 14
- between 5.5 and 9 is the physiological pH zone, in which an acid or basic chemical product will not be dangerous for human tissues.
Other types of lime (NHL-Z grade lime, HL artificial hydraulic lime, dolomitic lime…)
The use
Quicklime or slaked lime is widely used in various industrial sectors. We can find them for example in:
- agriculture (soil liming…)
- chemistry (pH adjustment…)
- construction (bleaching, soil stabilization…)
- water treatment (pH adjustment…)
- steel industry (iron conversion, impurity removal…
In the construction industry, lime and cement represent traditional masonry materials.
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Lime is a disinfectant material that emits no pollutants. It can be used inside as well as outside while promoting hygrometric exchanges. A frontage with an exterior lime will be impermeable to rain. Lime also has a high tensile strength of adhesion. Thanks to its various properties, lime is used more and more in the manufacture of cements, adhesive mortars and other applications.
When working with lime, it is important to follow the instructions on wearing PPE (personal protective equipment) such as helmets, gloves or protective masks.
The chemical risk
Contrary to thermal burns which remain a simple transfer of calories by radiation and conduction, chemical burns involve real molecular reactions. The chemical burn results from a reaction between the constituents of the eye, the skin or the mucous membranes and a corrosive or irritating classified chemical aggressor. There is a donor-acceptor exchange between two simple entities. This exchange corresponds to redox, acid-base, chelation, addition-substitution or solvation reactions. In the case of lime, the exchange will be of acid-base type.
The formation of the chemical burn consists in 3 steps:
- contact between the tissue and the chemical
- diffusion of the chemical in the tissue
- reaction between the product and the target biological compounds
The severity of the injury will depend on the nature of the product, its concentration, its temperature, and especially on the time of contact of the product with the skin, the eye or the mucous membranes.
Whatever the type of lime, this irritating or corrosive material is dangerous for humans. Its wide use and its chemical properties make lime a compound often responsible for serious eye, skin or respiratory burns. Moreover, the types of exposure are varied because of its different possible physical forms (solid, dust or solution).
Hazard classification of quicklime and hydrated lime in the GHS (Globally Harmonized System):
- H315: Causes skin irritation
- H318: Causes serious eye damage
- H335: May cause respiratory irritation In the case where slaked lime contains crystalline silica:
- H350: May cause cancer (inhalation)
Contact with the eyes
Quicklime or slaked lime in contact with the eyes may cause effects ranging from moderate eye irritation to chemical burns that may result in blindness (total visual impairment). Moisture in the eyes will promote penetration of the substance if it is in powder form and the creation of the chemical burn.
Skin Contact
Pain may appear hours after exposure when a significant injury has already occurred. As a result, victims may not be immediately aware of the hazardous exposure. A contact with lime can cause burns ranging from simple dryness or irritation to irreversible chemical burns that will require medical attention.
Inhalation
Inhaling large volumes of lime can cause chemical burns of the nose, throat or lungs.
Focus on the construction industry
The high alkalinity of lime in cement is an important factor in chemical hazards in the construction industry. Cement is a corrosive product with a high basic pH (12 to 13). Although a brief exposure causes little risk, exposure to dry or wet cement for a sufficient period of time may cause irreversible damage to the respiratory tract, skin and eyes.
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While the construction industry accounts for only 12% of lime use in the EU, it is reported by emergency and burn services that cement accounts for a significant proportion of chemical injury victims. People who work with cement are often exposed to it due to the lack of adequate protection.
Example of skin contamination
The lime dust got in between the pants and the worker’s boot. He did not notice it. As a result, no washing was done. After 2 days, a burn as shown in the picture appeared.
When lime comes into contact with the eyes, the worker is immediately bothered either by the dust or by the chemical action that takes place and creates pain. When it comes in contact with the skin, the pain is not immediate and the worker tends to pay less attention. However, it is essential to wash off the chemical quickly because lime, due to its corrosive or irritant nature, will not fail to create a burn. The longer the contact time, the deeper and more serious the burn will be.
How to protect yourself from contact with lime?
There are different types of PPE (personal protective equipment) adapted to the risks you encounter in your activity (e.g.: a harness for working at height, earplugs against noise,…). To protect yourself from chemical products, you can find the classic goggles, gloves, overalls, full body suits, but also special equipment adapted to a specific handling. When handling lime, chemical protective gloves that comply with the EN ISO374-1: 2016 standard and PPE Regulation 2016/425 are required. It is also important to respect the maximum time for wearing these gloves.
Therefore, remember to check the adequacy of your personal protective equipment, to wear it and adjust it correctly. If a PPE should fail (e.g.: hole in the glove, chemical product that goes under the glasses or that runs on the face) you must react quickly to wash and avoid that the product has time to penetrate and react.
Contact with lime, what to do?
- Get out of the way of danger
- Take off your clothes
- Decontaminate yourself
- Alert
- Seek Medical advice
How to decontaminate ?
DIPHOTERINE® solution allows for the rapid removal of the chemical present on the tissue and which has not yet reacted with the tissue in order to avoid or limit its action. Thus, the extent and severity of the chemical injury is prevented or limited and, if necessary, secondary care can be initiated. DIPHOTERINE® Solution is a medical device for washing the eye and skin in case of contact with an irritating and/or corrosive chemical, for use on healthy and injured tissues, in accordance with the EN 154154-3 & -4 standard. If DIPHOTERINE® solution is not available, use water according to the EN15154-1 & -2 standard. Unlike DIPHOTERINE® solution, passive washing with water has no effect on the chemical that has already penetrated the tissues.
It is imperative to consult a medical professional after the use of a first aid solution. In case of hydrofluoric acid and fluoride splashes in an acid environment, use solution HEXAFLUORINE®.
Caution!
Lime splashes in the eyes? The use of a phosphate-based decontamination solution is not recommended! Buffer solutions containing phosphates on an eye injury can cause calcification of the cornea. Calcification is a precipitation (formation of a solid) in the cornea. This causes an opacification of the cornea and a loss of vision. Only a surgical intervention can then help the victim. As lime contains calcium, the risk of such a phenomenon occurring is greatly increased.
DIPHOTERINE® and HEXAFLUORINE® solutions do not contain phosphates and can be used safely with any chemical in contact with the eyes.
Sources :
1 : European Lime Association (2020). EuLA 2019-2020 Activity Report : https://www.eula.eu/2019-2020-eula-activity-report/
2 : Schrage F., Schareck B., Kompa S., et al. Comparaison of emergency eye-wash products in burned porcine eyes (2002) . Graefe’s Arch Clin Exp Ophthalmol 240 :308-313
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