Occupational Health Tools 2009
Clean air - 1.3 Gases and Fumes
Carbon Monoxide
What is the problem?
Carbon monoxide (CO) is a deadly poison – colourless, non-irritating and odourless.
Apart from causing death, over 10% of survivors are left with a brain injury.
The traditional view of carbon monoxide poisoning – the production of carboxy-haemoglobin preventing access of oxygen to cells – gives an incomplete picture of the toxicology. Evidence as to best treatment is unclear, so prevention is of great importance.
Carbon monoxide poisoning is the most common industrial poisoning in the USA – from the use of things like forklifts and concrete cutting saws and compressors in buildings or semi-enclosed spaces such as garages. It can be deadly even when ventilation appears adequate.
Problem assessment
Carbon monoxide monitors – both ‘personal’ and ‘general air’ – are available but should only be used to signal the need to immediately exit a confined area.
Control measures
- elimination of fuel-powered motors in confined spaces
- placement of fuel-powered motors away from air intakes
- ventilation
- learn the symptoms of carbon monoxide poisoning: headache, nausea, weakness, dizziness, visual disturbance and loss of consciousness.
- look out for workmates.
Fibreglassing
What is the problem?
Exposure to airborne solvents (styrene and methyl ethyl ketone (MEK).
The potential for exposure to a wide variety of other chemicals: resins and hardeners; catalysts and initiators; fibres and reinforcers; mould release agents; fillers and pigments; inhibitors; and promoters and accelerators.
All are used and may enter the body via the respiratory tract or the skin.
Dust exposure may also be a problem.
Problem assessment
Exposure to solvent vapours in this industry causes a lot of ill health. The problem should be treated as potentially serious. Air monitoring is appropriate only where processes are constant. Biological monitoring is possible.
Control measures
Control air contaminants at source:
- local exhaust ventilation
- ventilated booths
- low-emission guns
- work behaviours
- housekeeping practices and
- appropriate PPE.
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.
Reference
The Pest Management Association of New Zealand has a code of practice that is available to members only. It is possible that this will be approved by ERMA and thus become a public document in time. See www.pmanz.co.nz.
Hydrogen sulphide
What is the problem
This is a very toxic gas (like cyanide) and can cause rapid ‘knockdown’ and death.
Hydrogen sulphide is a potential hazard in tanneries, tanning abattoirs, mining, metal processing, the brewing and fishing industries as well as oil drilling or refining and the chemical, pulp and paper industries.
Other sources include industrial waste, facilities for domestic animals, sewers, natural and volcanic gas, and some hot springs (including the Rotorua thermal region). Confined spaces can increase accumulation and be rapidly fatal.
At low levels, complaints relate to odour, eye or respiratory tract irritation, nausea and headache. Around 250 ppm and above for a minute or more can cause severe breathing depression, fluid in the lungs, depressed circulation, and seizures. Rapid unconsciousness and fatalities can occur at over 700 ppm.
The odour (of rotten eggs) can be detected at low levels (under 1 ppm) though in some is not recognised until 1 to 10 ppm. However olfactory fatigue (i.e you can’t smell it any longer) occurs at about 50 ppm, and can develop within 10 minutes at about 100 ppm. This has obvious serious consequences.
Prolonged exposure can occur if disappearance of odour is mistaken for the dissipation of the gas.
Problem assessment
Hazardous situations include opening doors of pelt processing drums, which has resulted in collapse, coma, and convulsions. Mixing of sodium, calcium or other sulfides with acidic solutions can generate the gas. Agitation of solutions containing hydrogen sulfide may dramatically increase its air level.
Meters are available that indicate hydrogen sulphide concentrations in the air. Often these combine a ‘low oxygen’ warning feature.
Control measures
- Confirmation of the atmosphere before entry to areas of known or suspected hazard (including confined spaces such as manure pits and sewers) is essential.
- Where levels are elevated or unknown, use air supply (NOT air purifying) respirators, with sufficient supply taking into account the time required for exiting confined spaces.
- Wear personal alarms.
- Provide emergency rescue arrangements – if the prior risk assessment shows that the hydrogen sulphide levels in a confined space can rise.
- Do not attempt initial rescue unless wearing adequate respiratory protection. Self-contained breathing apparatus (SCBA) is indicated for poorly ventilated, enclosed areas and/or when the gas concentration is unknown. A positive pressure airline respirator is satisfactory under other circumstances.
- Rescuers should have secure escape routes, safety harnesses and lines, and be observed by other (similarly protected) personnel, outside the area (‘buddy system’).
Isocyanates
Isocyanates are chemicals used in:
- the production of polyurethane foams : e.g. foam mattresses and rigid foams in chairs etc.
- paint and lacquers in motor vehicle repair – in 2-pack paints in which isocyanate hardener or activator is added to a pigmented or clear base.
- some adhesives.
What is the problem?
A single, high exposure to isocyanate vapour, aerosol or dust may cause immediate effects such as irritation to the eyes, nose and throat, resulting in coughing and a dry throat.
More severe effects can include chemical pneumonitis. Such a high exposure can cause immediate sensitisation, resulting in occupational asthma.
A series of smaller exposures over weeks, months and years may lead to wheezing, coughing, shortness of breath or a tight chest, symptoms of asthma.
Contact dermatitis may occur from skin contact with un-reacted isocyanates.
Exposure to isocyanates may occur via:
- Inhalation of vapour – espe-cially from TDI class isocyan ates which are very volatile (TDI = toluene di-isocyanate)
- Inhalation of airborne droplets from spraying or spray painting
- Inhalation of dust while handling pure MDI (MDI = methylene bisphenyl isocyanate)
Isocyanates can react violently with alkalis and acids e.g. sodium hydroxide, ammonia. They also react (slowly) with water and this can result in a dangerous build up of pressure in closed containers.
Problem assessment
Employers should carry out air sampling to assess the risk. An exception is in spray booths where operators are wearing a full face airline respirator (as exposure outside the mask would be expected to be above the exposure standards).
Where a ventilated spray booth is being used, assessment of the airflow in the booth can be carried out and compared to New Zealand Standards. Pre-employment lung function testing is recommended and annual lung function testing and medical exam is required.
Controls
As always, the first steps in control should be substitution/elimination, isolation then minimisation. Minimisation controls include:
- local exhaust ventilation for spray painting
- use ventilated booths
- spray-painters - do not remove visor or hood before ventilation clears the spray booth of mist and do not remove respirator before leaving the booth
- safe cleaning practices e.g. of spray guns good housekeeping
- appropriate PPE appropriate training
The Isocyanate Code of Practice requires air testing where TDI and MDI are being sprayed. Air monitoring should be discussed with a hygienist before being recommended or carried out.
References
DOL Approved Code of Practice for the Safe Use of Isocyanates.
New Zealand Standard for spray Booths AS/NZS 4114:2003.
Solvents
Organic solvents (e.g. toluene, white spirits) and products containing solvents are used in many workplaces. They can enter the body through the lungs, the skin or by being swallowed.
Common effects are:
- headaches
- weakness
- forgetfulness
- irritability and mood changes
- nausea
- damage to the skin and eyes
- giddiness
- abnormal tiredness
- drowsiness
- balance disturbance
Different people react differently to solvents. Not all solvents have the same effects.
These effects may disappear once you stop work with solvents, but long-term or high exposure increases the risk of permanent damage.
Long-term exposure can damage the nervous system resulting in:
- lack of concentration
- memory loss
- blunting of mental skills
- depression.
Skin:
Solvent contact with skin often causes drying, cracking, reddening and soreness. It increases the absorption of solvents and encourages skin infection. Dermatitis caused by solvent use may last a long time, even when you stop using solvents.
Lungs:
Many solvent vapours irritate the lining of the respiratory tract, affecting the nose, throat and lungs. In certain conditions, some solvents may cause an asthma-like attack.
Eyes:
Solvent vapours or liquids may cause eye irritation. This is usually reversible and permanent damage is rare. Solvent splashes to the eyes are dangerous and must be treated immediately.
Reducing solvent exposure
Employers must provide adequate ventilation. Exposure to solvents can also be reduced in other ways, e.g. by:
- using other products in place of solvents
- using a less volatile solvent (one that evaporates more slowly)
- using a less toxic solvent
- reducing the quantity of solvent used
- keeping containers sealed
- cleaning up spills immediately
- placing solvent-contaminated rags in a sealed bin.
Protective equipment:
If exposure to solvents cannot be avoided you must use personal protective equipment. If working in an area where mechanical ventilation is not practicable, wear a correctly fitted and selected respirator.
Spraycoating
What is the problem?
Spray painting results in exposure to hazardous substances including:
- Paints
- polyisocyanates
- solvents
- degreasers
- powders
- paint removers
- Dusts
- glues
- lacquers
- surface preparation products
- Resins
- rust converters / removers.
Other hazards include:
- plant
- electricity
- paint injection
- noise
- airless spray guns
- manual handling
- risk of fire and explosion.
Health effects can include:
- occupational asthma
- allergic dermatitis
- lung cancer
- painter’s syndrome or solvent neurotoxicity (from long-term exposure to organic solvents and affects the brain)
- damage to the reproductive systems, kidney and liver.
Short-term effects can include:
- irritant contact dermatitis
- burns to the skin and eyes
- vomiting and diarrhoea
- irritation to nose, throat, lungs
- headache, dizziness, nausea and fatigue.
Problem assessment
Risk assessment involves working out the level of risk from each hazard in the spray-painting process: how long is the person exposed? how great is the exposure? what harm might occur and how severe could it be?
Control measures
Spray Booth
Spray-painting must be carried out in a spray booth unless, because of its shape, size or weight, it is impractical to do so; for infrequent spraying of heavy or bulky equipment; or minor operations such as spotting or touching up. The spray-booth must be designed, constructed, installed and maintained in accordance with AS/ NZS 4114.1:2003 Design, construction and testing of spray-booths; and AS/NZS 4114.2:2003 Selection, installation and maintenance of spray-booths.
Exclusion zone/confined space
A spray-painting exclusion zone should be established according to AS/NZS 2430.3.9 1997: Classification of hazardous area: Part 1: flammable gas and vapour atmospheres. Spray-painting in a confined space must be carried out as per AS 2865: 2001 Safe working in a confined space.
Spray booth/mixing room ventilation
The ventilation system should provide an optimum, continuous, uniform and evenly distributed supply of airflow throughout the spray-painting area and mixing room to the exhaust outlets and eliminate pockets of still air in the booth. Where spray-painting is carried out in a building or structure other than a spray booth or confined space, it should be of open construction or a mechanical exhaust system should be used to prevent the build up of flammable or toxic fumes.
Spray-painting guns
High-volume-low-pressure (HVLP) spray guns are recommended over conventional gravity or siphon-feed guns because HVLP guns cut paint over-spray concentrations in half. HVLP guns transfer paint more efficiently and can reduce paint usage.
Respiratory protection
Even the best precautions do not completely eliminate overspray from the air workers breathe. Personal respiratory protective equipment is also recommended.
References
NZS/AS 1715:1994 and AS/ NZS 1716:2003 Selection, use and maintenance of respiratory protective devices, and
NZS/AS 1716:1991 Respiratory protective devices). The current Spraycoating Regulations date back to 1962 and are being revised.
Welding
The common processes are:
- Gas - brazing, oxyacetylene
- Electric - manual metal arc (MMA), metal inert gas (MIG), tungsten inert gas (TIG), submerged arc welding (SAW)
Airborne contaminants include:
- Dusts/Fumes - metal fumes, flux dusts, flux fumes. Some are extremely toxic (cadmium, beryllium)
- Products of combustion – nitrogen oxides (lungs), carbon monoxide (systemic), carbon dioxide (asphyxiant)
- Others - inert gases (from shielding gas), the toxic ozone and the highly toxic phosgene.
Risk assessment
If welding is being done at a workstation in an assembly line then air monitoring and appropriate analysis will give a good indication of exposure to fume/dust. Use a Tyndal Lamp to show dust plumes.
Welding may also be done in the open (a construction site) or in a large workshop (fabrication of a boat or steel components for civil engineering etc). In these settings risk assessment is harder.
Controls
1. Substitution of welding rods: some welding rods emit much less fume than others. Seek advice from the supplier.
2. Current control: follow preferred work practices. Keep the current to the minimum to minimize emissions.
3. Flame optimisation: following safe work practices reduces emission of contaminants such as carbon monoxide.
4. Local exhaust ventilation: possibilities include: fixed extraction hoods – for assembly line work portable ‘vacuum cleaner’ type extraction flexible, ducted extraction systems.
5. General air ventilation: Build-up of welding fumes can be unpleasant but can be avoided by having open doors and adequate ceiling extraction. There must be enough air changes per hour and no ‘dead spots’. General air ventilation is no substitute for local exhaust ventilation.
6. Work practice: – like keeping the head away from the rising plume of dust/fume generated by the welding process. Positioning the work piece and/or placement of the body are both obvious possibilities.
7. Personal protective equipment: UV visor – face shields (may be air-supplied for extended periods of work), gloves, overalls and aprons. Specialised help in selection and fitting is advised.
Confined spaces
Confined spaces increase hazard levels – through over-exposure, asphyxiation and oxygen deficiency.
Phosgene
Phosgene can be produced when chlorinated solvents are involved in welding process (e.g: if steel is not properly cleaned after degreasing).
Other hazards
Ultraviolet light; electrical hazards; hot metal particles; flammable gases; compressed gases; noise; heat stress; and manual handling.
Welding Fume Control Table
Add the three weightings you obtain from the Tables 1-3 to find out what control actions are needed from Table 4.
1 Process Weighting Factor
| Process | Weighting |
|---|---|
| Submerged arc welding (remote); laser cutting and welding; micro plasma; Gas cutting (remote operations). | 0 |
| Submerged arc welding (manual); submerged arc welding (multi arcs). | 2 |
| Brazing (manual operation); TIG (manual operations); gas welding and cutting (manual); silver soldering (manual); resistance spot welding (manual); plasma cutting (under water table); plasma arc welding; MIG (remote operation); resistance seam welding (remote operation); electroslag welding. | 4 |
| MIG (hand held); MMAW; Resistance seam welding (manual operation); thermit welding; electrogas welding. | 7 |
| Arc cutting; plasma arc gouging; air arc gouging; flux cored arc welding (manual and remote operation). | 9 |
| Plasma arc cutting | 15 |
2 Fume Constituent Weighting
| Fume Group | Weighting |
|---|---|
| A: Iron, aluminium, tin, titanium - < 5% of B or C. < 0.05% D | 0 |
| B: Copper, magnesium, manganese, molybdenum, silver, tungsten, zinc. Flux fumes such as fluorides, rosin, phosphoric acid, zinc chloride and boric acid | 10 |
| C: Barium, chromium, cobalt, lead, nickel, ozone, vanadium, phosgene, organic fume. | 20 |
| D: Beryllium, Cadmium | 55 |
3 Work Location Weighting
| Location | Weighting |
|---|---|
| Outdoors | 0 |
| Open | 12 |
| Limited | 16 |
| Confined | 24 |
Add the three scores and compare ...
4 Control Requirements
| Sum | Control Requirements |
|---|---|
| < 9 or 9 | Natural Ventilation |
| > 9 to 21 | Mechanical ventilation |
| > 21 to 54 | Local exhaust ventilation |
| > 54 | Local exhaust ventilation and respiratory protection |