Occupational Health Tools 2009
Clean Air – 1.1 Introduction
This first section is about workplace air contamination. Assessing and controlling the risks from the contaminants described are beyond any one person’s abilities.
The safety of employees relies on your being informed about these hazards and your alertness, intuition and experience in identifying their presence. Key points are:
- alertness to the possibility of air contamination
- recognition of possible types of contamination in different employment settings
- knowing basic risk assessment and control measures and
- knowing what to do when your knowledge runs out.
Points 1 and 2 rely on your being informed and your own abilities.
Point 3 is covered (in part) in this aide mémoire.
Point 4 requires that you refer on to a specialist.
Combining these, and using them with your existing health and safety system, will result in a systematic approach in your workplace to identify these hazards.
How have we selected these topics? Clean air is included to raise awareness and to emphasise that exposure to hazardous substances – including those that cause allergic reactions – is an ongoing no-no.
The topics are presented without prioritisation due to the scant information on which to assign priorities:
- some are potentially rapidly fatal but occur infrequently
- some are slow acting but have more frequent exposures and some
- create an allergic response with time.
There are five reasons for including these particular clean air topics in the booklet:
- Part of the Department of Labour 2008/2009 Priority Programme in Health:
- fibreglassing, carbon monoxide, silica, fumigation and solvents.
- Known pervasive problems:
- welding and solvents, etc.
- Potentially suddenly fatal problems:
- carbon monoxide, fumigation, hydrogen sulphide and oxygen depletion.
- Latency issues: ill health occurs some time afterwards:
- silica, solvents, asbestos, fibreglassing and lead.
- Profile needs raising for some exposures:
- organic dusts and occupational asthma.
Key principles of controlling workplace air contamination
1 Eliminate the substance or process producing the contaminant.
Substituting hazardous materials with non- or less-hazardous ones, by automation with enclosure or outsourcing can mean that:
- employers keep on-side with regional councils
- complaints from neighbours are eliminated
- the need for monitoring is eliminated (see point 4 below)
- ongoing costs for personal monitoring and assessment are eliminated
- the need for protective equipment and training is eliminated
- clean-up is easier
- fire hazard and, maybe, insurance costs are reduced and
- HSNO commitments are reduced.
2. Isolate the process
This can be achieved by automation and enclosed ventilation, using a booth, or isolating the person (e.g. in an airtight cab or control room).
3. Minimise exposure
Exposure to hazardous processes or substances which are not eliminated or isolated must be minimised by the use of ventilation, booths, PPE, damping with water, work practices and work techniques.
4. Control the contaminant at source
Contaminant control at source means ensuring the escape of contaminant to the atmosphere is minimised. This can be achieved with e.g.:
- local exhaust ventilation (see following section)
- keeping lids on volatile substances
- using automatic dispensing methods
Controlling at source results in:
- better control over airborne contaminants – reduced employee exposure
- energy efficiency - local extraction ventilation saves on power costs (as less air needs to be moved)
- loss control - by evaporation of costly thinners and solvents,
- lower ACC and sick leave liabilities.
5. Monitor exposure to significant hazards
If the employer judges that serious harm may result from exposure to any chemical and the exposure cannot be eliminated or isolated, then:
- the employer must monitor employees’ exposure and
- if there is a method for doing so (see page 40), you must (after getting their informed consent) monitor your employees’ health in relation to the chemical exposure.
General air ventilation (fan in the roof/open doors) is okay for some situations (e.g. piggeries) but is wasteful and ineffective for controlling airborne exposures from most industrial processes (e.g. spray-coating and welding).
6. Personal protective equipment (PPE)
Is not a cheap option
- is usually uncomfortable to wear – compliance poor training about when to use it will be needed PPE needs to be selected correctly, fitted correctly (using a fit test), maintained and replaced as it wears out.
- It must also be worn!
7. Information to employees
Provide clear information to employees about the hazards of what they are using and doing with it, what is happening to control clean air hazards and what their responsibilities are.
Types of air contaminants
| Type | What it is | An example and where you might find it |
| Dust | Tiny bits of solid material suspended in the air. | Wood dust in cabinet making or a craft woodworker using rimu; flour in a bakery; mould dust from bird droppings or compost. |
| Mist | Tiny droplets of liquid suspended in the air. | Acid mist at an electroplating shop; water spray near an air-conditioning unit. |
| Fume | Extremely fine metallic particles originating from hot processes. | Metal fume in a foundry or from welding process. |
| Vapour | Gas from an evaporating liquid. | Paint thinners during spray-coating; solvents from recently LOSP-treated timber; fibreglassing. |
| Gas | Carbon monoxide from the use of petrol-powered forklift used in a confined space. Methane from anaerobic decay of organic matter. |
Industrial Ventilation
Industrial ventilation means the use of supply and exhaust ventilation to control emissions, exposures, and chemical hazards in the workplace.
Traditionally, air-conditioning has been used to control temperature, humidity and odours. This more of a Building Certification matter.
Industrial ventilation is in 2 types:
1. Dilution ventilation
Where air is blown into a space to dilute contaminants and force them outside. This might be visible as a large fan on the ceiling of a factory [and is often thought to be all that is needed by many employers]. This type of ventilation is not energy efficient for controlling specific industrial processes being carried out in a factory because the amount of air required to dilute the contaminants compared to the size of the room is so great it uses a lot of power. Dilution ventilation must never be used to control toxic substances e.g. solvents, (some) welding fume, spray-coating vapour. Control at source is required.
2. Local exhaust ventilation (LEV)
systems capture contaminants as close as possible to their source (with a hood) and convey the contaminant through ducting with the contaminated air being discharged through a stack [chimney] via a scrubbing system (e.g. dust bag, bag house or electrostatic precipitator).
LEV is the preferred option, as it reduces the release of contaminants into the workplace and the potential for exposure.
LEV systems require specialist engineering knowledge in design, fabrication, installation, evaluation and maintenance.
LEV systems should capture the contaminant – this is a matter of hood design and placement. It must be positioned so that it draws contaminant away from the worker. Smoke tubes are very good for showing how well a hood captures a contaminant.
The velocity of air needed at the hood face will depend on the type of contaminant and how it is produced, e.g. metal particles produced from grinding are thrown out at high speed therefore require a high velocity to be dragged into the exhaust hood.
Deciding on the right air velocity and the type of hood to use should be done by a specialist e.g. a hygienist or ventilation engineer. It is usually cheaper and easier to design the ventilation right in the first place than it is to try and fix an ineffective ventilation system (that in the mean time may be providing little or no protection for workers).
Refer to a specialist when:
- the capture is inadequate – i.e. flow rates or hood position do not appear to capture contaminants,
- the hood appears to be badly designed,
- the LEV system leaks (dust or contaminant deposition on or around the ductwork),
- filters ‘appear’ to be overloaded.
Commonly encountered misconceptions
“They have ventilation so it’s all under control”:
Ask yourself/your client:
- is it working, is it used, can it do the job
- when is it used, does it have sufficient capture velocity,
- is it controlling at source,
- is it maintained (ask for records),
- are filters changed,
- is any contaminant escaping though leaks in ducting/hood,
- is the contaminant being taken away from the operator rather than towards their breathing zone (e.g. for hot processes, such as welding, the rising plume will invade the breathing zone if the hood is above the welder)
Case Study: A good example of futility is the ventilation system used in nail bars. Typically, a slot or grid in the table where clients rest their hands is exhausted through a tube and charcoal filter. Given the amount of solvent in the air (which can’t all be completely captured by this arrangement) the charcoal filters will need changing so frequently as to make the cost prohibitive.
“The vapour/gas is heavier than air so therefore the ventilation should be placed near the ground”
The biggest myth in the book!
The only time you will get a vapour/gas collecting in a pool at floor level is when you have completely still conditions and very high concentrations (higher than a person could work in) i.e. no drafts, no doors/windows open, no thermal gradients, no machines moving to create air currents or people moving around and no LEV. This situation is very rare in most industrial settings. It may occur in tanks/silos/ unused rooms. In all cases vapours/gases are best controlled at the source i.e. ventilation at the machine/task and since people generally don’t work at floor level this means it should be placed at working height.
Reference
Industrial Ventilation: A Manual of Recommended Practice (26th edition). American Conference of Governmental Industrial Hygienists (www.acgih.org)
Workplace Exposure standards
Workplace exposure standards (WES) refer to concentrations of airborne substances and represent levels to which it is believed nearly all workers may be exposed to repeatedly day-after-day without adverse effect.
WES are guidelines for those involved in occupational health practice. Their use by untrained persons as a marker in determining ‘compliance’ is not recommended.
Compliance with the WES does not guarantee protection from discomfort or ill-health outcomes for all workers. The range of individual susceptibility is wide and it is possible that workers will experience problems from exposure to substances at levels below the WES.
It is inevitable that some WES will be lowered in the future.
The workplace exposure standards are not to be used to differentiate between exposure levels that are safe or unsafe.
The relationship between the numerical value of two exposure standards cannot be used as a measure of relative toxicity.
Some standards are designed to prevent the development of ill health after long- term exposure; others to reduce the possibility of acute effects.
While substances hazardous to health may enter the body following inhalation, ingestion or skin absorption, it is usually the inhalation component that is most important.
The technical feasibility of limiting exposure varies from substance to substance and in practice this may restrict the safety factor that can be realised.
Note: Regardless of the WES, it is important to take all reasonable steps to reduce the concentration of airborne substances to the lowest practicable level.
DOL Reference
Workplace Exposure Standards.
Clean air - 1.2 Dusts
Arsenic
What is the problem?
Timber treatment (e.g. with CCA) and its downstream use may cause exposure to arsenic and other chemicals.
Problem assessment
Environmental measurements can indicate the concentration of arsenic in the breathing zone.
Biological monitoring involves urine testing for inorganic arsenic plus its organic metabolites (dimethyl arsenic and methyl arsenic acids), while abstaining from seafood for a few days prior to testing(!) This is best done at end of a shift at the end of the week. The BEI is 100 µg/L. (~1.3 µmol/l).
Control measures –
Timber treatment
- Integrity of the process and the plant
- adherence to operating procedures - implied elimination of contact with chemicals.
- Drip-free exit from pressure vessels.
- Subsequent handling of wet timber requires waterproof gloves, overalls and aprons.
Subsequent usage
- Sawing, (plus maybe though unlikely routing and planing) of treated timber may cause airborne dust but the risk is time dependent — and will be significant only if it goes on long enough.
- Prudent avoidance (only) is advised — wearing gloves and dust masks when sawing, routing and planing.
- Hand hygiene.
DOL References
1. Approved Code of Practice for the Safe Use of Timber Preservatives and Antisapstain Chemicals
2. Working with Timber Treatment Chemicals
Asbestos
What is the problem?
Asbestos exposure can cause serious lung diseases (asbestosis, lung cancer and mesothelioma) and cancers in other parts of the body.
Asbestos is found in brake and clutch linings and in certain building products formerly used in New Zealand. These products include asbestos cement cladding, textured ceiling coatings, thermal insulation around pipes and boilers, and fire-protective linings on structural steel (limpet asbestos).
Asbestos exposure can occur during: its removal demolition work floor sanding car repair work (brake linings)
Problem assessment
Laboratory analysis will be required to see if a suspicious fibrous material contains asbestos.
The Asbestos Regulations
Work with asbestos is regulated under the Health and Safety in Employment (Asbestos) Regulations 1998.
These Regulations specify particular tasks involving asbestos as restricted work that must be notified to the Department of Labour before work begins.
These tasks must be carried out by a person holding a certificate of competence for this work, or by someone under direct supervision of a person holding a certificate. The regulations also specify controls that apply to anyone working with asbestos.
Control measures
Where contact with asbestos-containing products cannot be avoided, then all practicable steps must be taken to minimise exposure to asbestos fibres. This may be achieved by:
Ensuring that effective steps are taken to stop or limit the release of asbestos fibres into the air. Ensuring that sound work practices are used to avoid the spread of asbestos contamination on clothing and footwear (wearing disposable outer clothing is recommended). Use dust extraction equipment where the generation of fibres from a process cannot be avoided. Where all other steps have been taken, and the possibility of excessive exposure remains, minimise the inhalation of asbestos fibres by using appropriate respiratory protection.
Health surveillance
Due to the particular hazards of work with asbestos, it is essential to monitor employees who carry out restricted work with asbestos.
This monitoring may include chest x-rays and lung function tests. The DOL Departmental Medical Officer may also require any other person undertaking work with asbestos to have a medical examination.
Employees who may have been exposed to asbestos are also invited to enter their names and appropriate exposure details in the Asbestos Exposure Register administered by DOL.
Hard Metal Disease
What is the problem?
Milling tungsten carbide tips (during saw sharpening) can cause airborne dust concentrations great enough to lead to ‘hard metal’ lung disease. Cobalt (a binder) is considered a crucial factor in producing this disease, though this may involve an interaction with the tungsten carbide itself. Fluxes used in the brazing process (when the tips are attached to the saw blade) can cause respiratory reactions (this is a separate issue).
Problem assessment
Environmental measurements can indicate the concentration of airborne dust. Analysis for cobalt should be carried out on the dust sample. WES = 0.05 mg/m3.
A BEI of 15 µg/l (urine) and/or 1 µg/l (blood) has been proposed for this metal, samples to be taken at the end of work shift at end of week. The worker should also undergo periodic health surveillance, including lung function tests. A questionnaire was compiled by the Department in 2001.
Control measures
- Local exhaust ventilation – to control the spark shower from dry grinding processes.
- Wet mist ventilation in automated sharpening is common in sawmills.
- If neither is in place, use PPE.
Lead
Foundries, battery manufacture, radiator repair, paint stripping, sundry casting (fishing sinkers).
What is the problem?
Airborne lead dust can cause lead poisoning. Ingestion is also a significant route of exposure.
Problem assessment
Environmental measurements can indicate the concentration of lead in the breathing zone. Biological monitoring is available. WES = 0.1 mg/m3. Lead in blood – 1.5 µmol/l in red blood cells Lead in urine – 0.72 µmol/l action level.
Control measures
Generic control measures include: strict hand hygiene, the use of PPE (see below). Biological monitoring indicates the level of lead absorption and is required when people are exposed to lead routinely.
Foundries:
Lead paint can contaminate ferrous metals and brass scrap contains lead. Gas cutting/gouging and furnace heat may produce lead fume. To control these exposures, use enclosed processes and local exhaust ventilation where possible. PPE should consist of the above plus the appropriate lead fume respirator.
Battery manufacture:
Where possible isolate via automated and enclosed processes; minimise through properly designed and maintained local exhaust ventilation; and use damp processing.
Radiator repair:
Very occasionally you may find a gas torch being used to disassemble a radiator. If so, and if exposure is ongoing, seek advice from the Department of Labour. Temperatures > 330, the melting point of lead, are needed. Check the biological monitoring status of the exposed worker.
Paint stripping:
Sanding or removal of paint from old houses with a blowtorch can produce lead dust and fume. Identify the presence of lead with a test kit from a paint shop.
Use a wet process where possible but prevent lead leaching into garden soil as it could go on to cause sickness in children or pets.
Use PPE – an appropriate respirator for dust or fume, overalls, hair covering and gloves.
Take care to prevent secondary exposure when taking clothing off and laundering.
Sundry casting
(e.g. boat keels, fishing sinkers): Avoid exposure to fume and dust with good ventilation and PPE.
Leadlight windows:
Avoid exposure to fume and dust with good ventilation and PPE.
Loading ammunition:
Avoid exposure to dust with good ventilation and PPE.
Personal protective equipment:
Appropriate (dust or fume) respiratory protection; overalls; apron; gloves; hair covering. Do not expose anyone to dust when taking off or laundering PPE.
Hygiene:
Strict attention to hand hygiene and other hygiene practices is required to prevent ingestion.
References
- Guidelines for the Medical Surveillance of Lead Workers
- Repainting Lead-Based Paint
- Lead Hazards in Radiator Repair
- Guidelines for the Medical Surveillance of Lead Workers
- Guidelines for the Management of Lead-Based Paints
Silica
Foundries, abrasive blasting, quarries mines, road making, concrete cutting.
What is the problem?
Silica dust can be present in the settings listed due to the use of sand or when rock is crushed. Continued exposure can produce serious lung disease.
Problem assessment
Employers should carry out air sampling to assess the level of risk.
WES = 0.1 or 0.2 mg/m3 respirable/ inspirable dust depending on crystal type. Analysis of solid samples of parent rock or sand can show its silica content and may help to predict whether air concentrations of dust are likely to be hazardous or not. New Zealand sands are usually high in silica, but most sandblasting appears to be with silica-low or silica-free sand or glass beads.
Control measures
Foundries
Substitution of silica-free sand may not be possible. Instead, local exhaust ventilation, enclosure of processes and the informed use of personal protective equipment (PPE) should be undertaken.
Abrasive blasting
Substitution by silica-free alternatives is widely practised. Properly designed booths and PPE should be used.
Quarries and mines
- road making:
- process isolation
- positively pressurise vehicle cabs and process control rooms
- water damping where possible
- use of PPE when outside
- adequate dilution ventilation.
Concrete cutting
Use of wet processes. In confined spaces – damp dust before sweeping up.
Wood dust
What is the problem?
The most serious concern relates to the risk of cancers of the nose (adenocarcinoma) and sinuses (ethmoid), which have been observed historically with exposures to hardwoods (beech, walnut, oak, mahogany, maple). The risk from soft woods is considered much less, but should not be entirely discounted.
Some wood dusts can cause allergic respiratory disease (e.g. asthma, sinusitis, alveolitis), and/or or allergic dermatitis. Implicated components include resin acids (plicatic, abietic and pimaric acids) rosins (colophony) and terpenes (pinenes and carenes).
Wood can be contaminated by microorganisms including fungi or microbial products (e.g. endotoxins) which may cause other lung reactions. Remember the potential for dust explosions.
Problem assessment
Furniture manufacturing and joinery have high dust exposures. Assess by air sampling and comparison with the WES. Use a Tyndal Lamp to indicate the efficiency of controls.
Control measures
- Avoid the indiscriminate use of compressed air to remove dust
- Isolate fine dust producing process
- General housekeeping
- Appropriately designed hoods and extraction devices mounted directly onto individual powered equipment
- Capture of dust as close as possible to the source of emission
- Adequate PPE for high-risk tasks
- Remove dust from flat surfaces
- Regular maintenance of ventilation systems.