Basic concepts in hazardous chemicals: Exposure

By Wan Zainal Azman Wan Abdullah
The Sun, April 13, 1996

The first step prevention injury is the identification of the hazardous chemicals. Although the precise nature of the hazard need not to be known, this would assist in the choice of the preventive measure to be adopted. How the exposure takes place - inhaled, absorbed through the skin or ingested - is also important. There are several general principles to be employed in industrial hygiene and occupational health to decrease exposures.

Substitution

This calls for the replacement of a toxic chemical with one that poses less hazard. The decrease in hazard may be a result of substitution of a less toxic compound or different physical properties (e.g. vapour pressure) without any change in the inherent toxicity of the material. Other factors such as skin permeability, bio-persistence and viscosity are also taken into consideration.

For example, toluene di-isocyanate (TDI) has hazardous effects on the lungs. A suitable substitute now exists - methylene di-isocyanate (MDI) - which is less volatile than TDI (provided that temperatures are kept below 45 degree Celcius) and therefore safer to use in the production of polyurethane foam.

Education of workers

Education is most vital. The most toxic compound can be put to use if the danger is known and sufficient precautions are taken. It is enough for a worker to know what work practices are recommended because unless the reasons are understood, the worker may intentionally deviate from these practices to save time or trouble. The industrial hygienist must understand that too.

It is self-defeating to except a worker to wear a mask, goggles, gloves and other protective gear when the temperature is 43 Degree Celcius. A worker who complies would be in increased danger of heat stress. If the operation is done outdoors, it should be delayed until the temperature drops. If it is done indoors, an engineering solution to prevent exposure should be indicated.

The first requirement of safety training is through the recognition of danger. Most chemicals are toxic to some degree and care in handling all types of chemicals should be a routine practice.

Misrepresenting or underestimating a particular danger leads to carelessness accidents. Specific information in the safety training of employees include methods of determining an exposure or release of a chemical. This determination may be the result of periodic monitoring done by the employer or the use of continuous monitoring systems. The employee must understand the physical and health hazards associated with the agent(s) in question.

From a preventive viewpoint, employees must be trained to understand the elements of good hygiene to minimise exposure to, and therefore ill effects from, chemicals. Personal protective clothing, emergency procedures, containment systems, and other means of reducing contact with the chemical should be understood by the employee. Information on the labelling system in use must also be part of the education.

Personal Protective Devices

This devices are generally seen by workers as cumbersome and an impediment to their ability to perform their job. The use of such devices are prone to failure unless there is sufficient employee education and compliance. All too often, workers are uncomfortable using the devices. This may occur because of unrealistic production demands on the workers.

Filtering systems are available for non-toxic dust, organic vaopurs, acid vapours, carbon monokxide, etc. In the selection of a system, it is essential to be certain that the particular contaminant will be effectively filtered by the device.

Protection of the eyes and face is also necessary. The protection needed depends on the job operation being conducted, materials involved and the severity of the eye or face injury that could result. The most common types of eye and face protective devices include spectacles, spectacles with side shields, goggles and face shields. Workers wearing contact lenses should avoid chemical atmospheres. These lenses may trap and increase the duration of chemicals in the eyes.

Workers should be instructed to remove contacts immediately if there is redness of the eye, blurring of vision, or pain in the eye.

Chemical protective clothing is designed to protect the skin from exposure of gaseous, liquid and particulate chemical hazards. It includes gloves, boots, aprons and full body protection.

Materials used to make chemical protective clothing include natural rubber, synthetic rubber, neoprene, vinyl, polypropylene and polyethylene films as well as fabrics coated with these materials. Protective clothing with long break-through times, low permeation rates and no degradation should be chosen. Some points to keep in mind when selecting chemical protective clothing are:

  • All chemicals will permeate a protective barrier given enough time.
  • Permeation can take place without any visible indication.
  • A material that protects against one chemical may not protect against another different chemical.
  • No single protective material is an absolute barrier against all chemicals.
  • Do not depend on color and appearance when choosing protective materials.
  • Once a chemical has permeated a protective material, it will continue to pass through the material.
  • If the protective material is contaminated by breakthrough, it must be decontaminated before being reused or disposed of.
  • The best way to select the proper chemical protective clothing is to test the material against the chemical(s) you are using.

Protective footwear is also necessary. Rubber or plastic boots are used when working in wet or muddy conditions or where exposure to chemicals is likely. Choose boots that will provide the best protection for the chemicals being used. These boots can be ankle high or extend over the entire thigh. In some situations, waist-high boots are used.

Protective Practices

No strict separation should be made between protective practices and devices. Either one or the other may be of predominant importance in a given situation. Here are some examples of protective practices:

  • Avoidance of exposure. Exposure can be avoided by simple procedures, for example spraying pesticides downwind or using a paddle instead of a hand to mix formulation.
  • Maintenance of equipment. Proper maintenance of equipment may minimise day-to-day exposure or prevent a gross accident. For example, maintenance of the shut-off valve and pressure hoses of a pesticide sprayer will reduce leakage of chemicals into the operator's body.
  • Working in pairs or groups. The lone worker is in constant danger. Whenever possible, people who make, mix, or use highly dangerous chemicals should work in pairs so that they can check on one another and give help as needed.
  • There must be no eating, drinking or smoking in working areas liable to be contaminated with any form of hazard.
  • Before going home, a worker should wash/shower with the mildest cleansing agent available and where applicable, change clothes. Otherwise, he will simply take the hazard home to his family.

The writer is a Science Officer at the National Poison Centre, Universiti Sains Malaysia.


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