GAS & FUMES HAZARDS VOL II Formaldehyde Background Formaldehyde is a colourless, flammable gas with a strong, pungent odour. It is sold mainly as an aqueous solution called formalin, which is 37% to 50% formaldehyde by weight. Formaldehyde is used to produce synthetic resins such as urea- and phenol-formaldehyde resins – used primarily as adhesives when making particle-board, fibreboard, and plywood. Embalming fluids contain formaldehyde and its use is common in pathology labs. Health effects The International Agency for Research on Cancer (IARC) has recently declared formaldehyde a human carcinogen. The first signs or symptoms (noticed at concentrations between 0.1-5 ppm) are burning of the eyes, tearing and irritation to the upper respiratory passages. Higher exposures (10-20 ppm) may produce coughing, tightening in the chest, a sense of pressure in the head, and palpitation of the heart. Exposures at 50-100 ppm and above can cause serious injury such as collection of fluid in the lungs, inflammation of the lungs (pneumonitis), or death. Dermatitis due to formaldehyde solutions or formaldehyde-containing resins is well recognised. After a few days exposure, a worker may develop a sudden inflammatory (eczematous) reaction of the skin of the eyelids, face, neck, scrotum, and flexor surfaces of the arms. An eczematous reaction may also appear on the fingers, back of the hands, wrists, forearms, and parts of the body that are exposed to the rubbing of clothing. This sometimes occurs only after years of repeated exposure. Minimising employee exposure Formaldehyde should be handled in the workplace as an occupational carcinogen. Exposure should be limited to as few employees as possible, and workplace exposure levels minimised. Exposure monitoring Initial and routine employee exposure surveys should be made to determine the extent of employee exposure and to ensure that controls are effective. Controlling employee exposure There are four basic methods of limiting employee exposure to formaldehyde. 1. Product substitution The substitution of an alternative (safe) material with a lower potential risk is an important method for reducing exposure. 2. Contaminant controls The most effective control is at the source of contamination by enclosure of the operation and/or use of local exhaust ventilation. 3. Employee isolation If feasible, employees may be isolated from direct contact with the work environment by the use of automated equipment operated by personnel in a closed control booth or room. 4. Personal protective equipment (PPE) The use of PPE, which may include respirators, goggles, gloves, etc.: during the time period necessary to install or implement engineering or work practice controls in work situations in which engineering and work practice controls have proven ineffective: for maintenance for operations which require entry into tanks or closed vessels in emergencies. Proper maintenance procedures, good housekeeping in the work area, and employee education are all vital aspects of a good control programme. Employees should be informed as to the nature of the hazard, its control, and appropriate personal hygiene procedures. Medical surveillance Health effects such as upper respiratory irritation or dermatitis should alert management that unacceptable exposure to formaldehyde is occurring. A medical surveillance programme should be made available that can evaluate these effects. In addition, skin protection should be stressed in the workplace to keep the number of new cases of dermatitis to a minimum. These comments also apply to glutaraldehyde. Fumigation What is the problem? Very toxic gases can be used. Processes are generally well regulated, but even short-term low exposures may cause (usually mild) symptoms, and considerable concern. Decisions have been made to gradually reduce methyl bromide production and use. (Recommended alternatives include metam sodium, dazomet, and chloropicrin. Sulfuryl fluoride has also been used in the United States). Handling of imported goods that are fumigated offshore has concerned port authorities and private consumers since methyl bromide can react with sulphur-containing materials (e.g. wool, furs, feathers and leather where sulphur is added during tanning) to produce volatile malodorous sulphur compounds. Transport and stacking of fumigated containers may be hazardous. Soil injection techniques (e.g. in fruit farming) are reputed to be safe, but studies suggest that levels under tarpaulins can take longer than 48 hours (the recommended minimum waiting period) to fall below 5 ppm. Magtoxin (magnesium phosphide) and similar (e.g. Al, Zn) phosphides react with water and (more readily) acids to form phosphine, a toxic gas with a garlic, fish-like odour. Used as a fumigant in preservation of stored grain (e.g. in grain elevators, marine vessels), often involving confined environments. In contact with moisture in grains, phosphine is generated along with metal (e.g. Al, Mg, and Zn) hydroxides. Phosphine has an auto-ignition temperature of about 40ºC, and when dry may occasionally ignite at room temperature, due to impurities. Aluminium and magnesium phosphide containers may flash on opening. (Many formulations contain ammonium carbamate or similar, which liberates ammonia and carbon dioxide, reducing the explosive hazard substantially.) Methyl bromide Mild methyl bromide effects include nausea, vomiting, headache, dizziness, slurred speech, unsteadiness (which can persist for some days) and also various neurological effects. Often chloropicrin is added as a warning agent as it is intensely irritating. There is a hazard from fumigated containers, particularly immediately upon opening. Such brief relatively low exposures may cause mild to moderately acute symptoms only but more severe (respiratory or neurological) effects are possible with high acute and/or regular long-term exposures. Levels can be assessed with automatic halogen ‘leak detectors’. These are non-specific, as they measure most (other) halogen gases as well. ‘Grab’ sampling (e.g. with Drager, Gastech tubes) is possible. Results should be compared with the WES-TWA (5 ppm). There is limited correlation between blood (inorganic) bromine levels and symptoms, and no BEI, but blood and/or urine levels are being investigated as monitoring tools. Air monitoring. Do not rely on odour as a warning. Control measures appropriate signage for fumigated areas precautionary monitoring if air levels unknown but potentially significant wear adequate respiratory protective equipment, especially when opening or entering containers ensure containers are sealed as well as possible check for leaks if suspected suitable protective clothing (methyl bromide can permeate many materials) education on phosphine explosion risk; especially if mixed with water or in confined spaces be aware of the symptoms of poisoning.
Posted on: Sat, 24 Aug 2013 08:45:30 +0000
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