Clean air - 1.5 Miscellaneous

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Multiple Chemical Sensitivity

If a person reports that they think they have the condition known as Multiple Chemical Sensitivity (MCS), there may or may not be a real condition. However, there is no way of proving or disproving it because the diagnosis basically rests on a person’s statements. Each diagnosis would be made on a case-by case basis. It is well known that what a person believes and expects about their symptoms can have an effect on the subsequent course of health events.

If MCS is accepted as a real medical condition, the exposures that provoke it may occur at many times below the Workplace Exposure Standard (WES).

The WES always acknowledges that some (a very few) sensitive people will suffer ill-health effects from exposures well below the WES, as the WES is set to protect only the great majority of people.

For example — the 8-hour noise exposure limit is set at 85dBA. The evidence suggests that, at this level, about 90% of people will be protected from noise induced hearing loss, but about 10% of people may experience some hearing loss, if exposures continue for 8 hours a day, 5 days a week and for a working lifetime.

This means that protecting all people against the levels that trigger symptoms of MCS would be prohibitively expensive, impractical for employers and probably not achievable.

The Department of Labour encourages employers to eliminate exposure altogether, which reflects the hierarchy of controls stated in the Health and Safety in Employment (HSE) Act 1992 — eliminate; isolate; minimise.

Where exposures cannot be eliminated, the Department encourages employers to make sure they are as low as is practicable.

Consequences for an employer

Employers are required to take all practicable steps to prevent harm. The definition of ‘practicable’ in the Health and Safety in Employment Act 1992 shows that the requirement for employers to protect employees is not absolute. What is practicable in each context will consist of a balance of a number of factors.

Ill health arising from gross exposures (i.e. at the WES or above it) are more likely, in the opinion of the Department, to produce symptoms that would be clear cut and to be diagnosed with terms other than ‘MCS’.

The Department would pursue standard compliance action under the HSE Act with employers where exposures were at the WES or above it.

Consequences for an employee

An employee who reported multiple chemical sensitivity would have to accept that there may be some environments where he or she could not work.

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Oxygen depletion

People entering a confined space may collapse and die if there is insufficient oxygen in the space to support life.

Normal air has about 21% oxygen and adverse health effects may be noticed if oxygen levels fall below 19%.

Effects may vary from person to person, but at levels of between 8-12% oxygen, rapid loss of consciousness and death can occur, unless the person is removed from the space and resuscitated.

Reduced oxygen concentrations initially cause increased breathing and heart rates, muscle in-coordination, emotional changes, and fatigue. More severe conditions can cause nausea, vomiting, loss of consciousness, convulsions, respiratory collapse and death.

Examples of confined spaces are offal pits, iron-walled compartments (e.g. ships where rusting removes oxygen) feed silos and sewers.

Sewers can also be a source of H2S.

Carbon dioxide (CO2) is an inert gas, but may displace oxygen in confined spaces and because it is widely encountered in industry, CO2 has been assigned a WES.

High levels of these gases can cause more rapid depressed consciousness than does a simple lack of oxygen. They should also be tested for in situations where they might be present.

Often the rescuers of a person collapsed in a tank or pit also die because they rush in without adequate protection.

Problem assessment

Identify, in advance, confined spaces where oxygen depletion may occur. Before entering a confined space, the atmosphere must be checked with a meter to see if it is okay to enter.

Control measures

• Confirmation of adequate oxygen in the atmosphere before entry.
• Emergency rescue arrangements if the oxygen content in the confined space can drop.
• Wearing personal ‘low oxygen’ alarms.
• Wearing oxygen supply equipment – that allows a limited time for exiting the confined space.

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Pesticides

What is the problem?

Rodenticides (designed for mammals) are generally the most hazardous group of pesticides. Careful handling is required with concentrated formulations (e.g. cyanide pastes). Repetitive exposures to some insecticides (e.g. organophosphates) can cause initially silent but gradually developing poisoning. Initial preparation (e.g. mixing of concentrates) and subsequent cleanup can involve high exposures, and protective equipment must always be worn. For some, skin can be a significant source of absorption, and clothing worn in hot weather is often insufficiently protective. Dermatitis may occur even with relatively low toxicity products.

Problem assessment

Air levels (e.g. mist +/- vapour with spray activities) are seldom measured and usually unknown. However, the spray methods employed, and the degree of usage and quality of personal protective equipment, plus work practices, provide circumstantial evidence on exposure. Blood or urine tests can be used in some cases. Most often blood acetylcholine-esterase monitoring is done for regular users of organophosphates but is less useful for carbamates. (Tests are also available for 1080; paraquat; 2,4-D and some others). Inadvertent ingestion is also a risk, and safe (child proof) storage practices are required.

Control measures

• Education (including availability of MSDS) and training in safe use (various courses are available).
• Should include the importance of reading labels (different precautions for different products depending on indicated level of hazard).
• Extra precautions with specific hazardous activities (e.g. mixing concentrate, fine droplet spraying of volatile constituents) or conditions (excessive heat, wind, dust generation).
• Adequate respirator selection, fit testing, cleaning, storage, maintenance and replacement practices.
• Adequate protective clothing, impervious where necessary.
• Biological monitoring programme where required (e.g. blood cholinesterase for those organophosphate users who work with sprays more than 30 hours per month).
• Secure storage of concentrates (lockable area).
• Adequate cleaning and segregation of boots and clothes (leave at work).

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Timber treatment

What is the problem?

Timber is treated with chemicals to kill insects and fungi to maintain the quality or life of the timber. This done with a variety of chemicals and methods including:

• CCA (copper, chrome, arsenic) preservatives
• Boron salt preservatives
• LOSP (light organic solvent preservatives) - usually tributyl tin oxide (TBTO) in white sprits.

The different methods and chemicals used present different exposure hazards.

Problem assessment

Exposure monitoring for the various products will depend on what chemicals were used in the treatment and where exposure is being assessed. Monitoring should be discussed with an occupational hygienist.

Employee health surveillance may be necessary, particularly where minimisation is used to control exposure. The surveillance required will depend on the treatment chemicals used and should be discussed with a DOL medical practitioner or occupational physician.

LOSP treated timber hazards:

LOSP treatment presents special hazards associated with the solvents used and the preservative (TBTO).

TBTO is a potent skin irritant and an extreme eye irritant, so skin and eye protection must be worn, at least until adequate drying of the timber has occurred.

The solvents can off gas for some time after treatment. Typical solvent in air levels and the flammability hazard are unknown. If adequate drying time is not given at the point of treatment, the plastic-wrapped timber can give off enough vapour when unwrapped to cause problems e.g. for employees in a truss and frame plant or a builder working in semi-confined areas.

Control measures

• adequate off-gassing time at the point of treatment
• filleting the stack of timber to allow airflow as it dries
• assessment of solvent residue at the point of use and consequent precautions if a problem is detected e.g. additional drying time in open air, general air ventilation etc
• use of organic solvent respirators
• when LOSP-treated timber is used in a confined space (e.g. at a closed-in house at a residential site) it must be substantially solvent-free first
• provision of information on chemical preservative products (including safety data sheets)
• detailed technical advice may be available from the Building Industry Association.

Ecology: Tributyl tin compounds are regarded as ecologically toxic. E.g their use as an anti-fouling agent in paints for ships hulls is banned.

Other control measures:

• substitution where possible
• specially designed plant
• ventilation
• personal hygiene
• PPE
• housekeeping
• appropriate training
• medical surveillance
• HSNO controls are applicable

Reference:

Best Practice Guideline for the Safe Use of Timber Preservatives & Antisapstain Chemicals: New Zealand Timber Preservation Council Inc. 2005

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Personal Health Monitoring

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Lung Function Monitoring

Monitoring lung function can be done with the following methods:

• Questionnaire
• Peak flow meter
• Spirometry
• Chest x-ray and other radiological investigations.

1 A questionnaire is cheap and easy and can be given as an initial screening tool by an inspector or health and safety representative. They will not be able to interpret the results which will need referral to an Occupational Health Nurse or Occupational Physician.

It can be used in any situation where there may be a potential breathing hazard present and is often performed annually. Questions can focus on symptoms such as cough, shortness of breath, wheeze, sputum production and exercise tolerance. Other important information includes history of exposure e.g: asbestos, allergens, dust, fumes.

2 Peak flow meters measure the maximum rate of expired air. They are cheap, simple and easily carried devices which can give useful though limited information. They can provide an indication of both the amount of airway obstruction and any variability of the obstruction over time. They can be used by an Inspector or Occupational Health Nurse.

For example, they can also be lent to the worker to record readings at both work and at home over a nominated period of time. Often a 2 week period is used to monitor if there is any variation throughout the working day or week e.g. when Occupational Asthma is suspected.

The worker blows hard and fast (<3 seconds) into the mouth piece to record the maximum rate of expired air. Three attempts are performed to get the best result. This result is compared with previous results or predicted values based on body size and age.

3 Spirometry measures airflow and lung volumes, and is the preferred lung function test. A spirometer is a much more complicated device than a peak flow meter and requires moderate skill to operate.

Spirometry is only worth doing if it is done properly by a trained occupational health professional. Spirometry records a number of different recordings related to lung function e.g. ‘FEV1’ and ‘FVC’.

Terminology

• FEV1 = the greatest amount of air that can be exhaled in the 1st second of exhalation
• FVC = the total volume of air that can be exhaled with maximum force, from maximum inhalation to maximal exhalation
• FVC & FEV1 are expressed as volumes (litres)
• They can also be expressed as a % of predicted values which are dependent on age, height, and gender.
• The ratio FEV1/FVC can be expressed as a percentage

Factors that influence normal values:

• Height - tall people have larger lungs
• Age - Respiratory function declines with age
• Sex - Lung volumes are smaller in females
• Race – Peculiarly, studies show Blacks and Asians as a whole have smaller lung volumes (-12%)
• Posture - little difference between sitting and standing. Reduced in supine position.

Spirometry helps detects two types of lung problem:

1 Obstruction

• A worker who develops Occupational Asthma e.g: after exposure to wood dust or isocyanate, will show obstruction, with reduced ability to expire or breathe out.
• FEV1 / FVC < 70%
• FEV1 < 80% of predicted value
• In severe of COPD the FVC may be less or much less than 80% predicted.

Assessment:

Severity	FEV1
Mild	> 70% predicted
Moderate	50 - < 69% predicted
Severe	< 50% predicted

 

2 Restriction:

• A worker with a pneumoconiosis e.g: asbestosis will show restriction with reduced lung capacity (smaller lungs).
• Both FEV1 and FVC < 80% BUT the FEV1/FVC ratio is normal or high.

Assessment:

Severity	FVC
Mild	>65 - 80% predicted
Moderate	>50 - 65% predicted
Severe	<50% predicted

 

Asthma

• Both FEV1 & FVC are reduced, but can demonstrate reversibility of at least 12%.

4. Chest x-ray and other radiological tests.

Chest x-rays are performed occasionally when clinically indicated. Eg Pneumonia, Asbestosis. They are ordered by a GP or Occupational medicine doctor.

Historically chest x-rays were sometimes performed as a screening test to detect early development of lung disease eg Asbestosis. This is not generally done now as it had a very low pick-up rate and it potentially can cause lung damage.

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Audiology

Hearing surveillance has three aims:

1. To identify people with hearing impairment or tinnitus and to prevent further hearing loss.

2. To monitor the effectiveness of noise control measures.

3. To detect the need for an education programme.

Hearing surveillance is a form of biological monitoring as it measures the impact of a hazard on the individual. As with all types of biological monitoring, the person being tested must understand the reasons for the monitoring, give their agreement and be informed of the results of the test. It is useful if the employee agrees to allow their manager to be informed of these results as they need to be able to identify people at risk when planning to control the risks in the workplace.

The Audiogram

As with most biological monitoring, it is important to obtain a ‘baseline’ by performing an initial audiogram. This identifies hearing loss present before the current employment and allows a more accurate assessment of the effects of noise in the current workplace. Two baselines are better than one.

DOL recommends that baseline testing comprises two audiograms at the following frequencies: 0.5kHz 1 kHz 1.5 kHz 2 kHz 3 kHz 4 kHz 6 kHz 8 kHz.

After the initial audiogram:

1. Audiograms should be performed regularly for all people working in an environment which has an established or suspected noise hazard, defined as an exposure level greater than 85 dB(A) Leq (8 hrs).

2. The baseline audiograms should be performed within 3 months of initial employment, after a period of at least 16 hours quiet. This could follow a period of absence from work or the wearing of high-grade hearing protectors to ensure that the exposure is no higher than 75dB(A). The beginning of a shift is often used to perform hearing surveillance.

These baseline audiograms provide the opportunity to:

• Educate the person
• Discuss the noise hazards in their particular area of work
• Discuss the programmes to control this noise and
• Explain the company’s or the practice’s policy on hearing surveillance.

3. Audiograms should be repeated no further apart than 2-yearly. They should be done more frequently where:

1. There is evidence of hearing loss
2. New processes have been introduced which pose a greater noise hazard
3. When requested by a specialist

4. Audiograms should be carried out in an environment where background noise is less than the levels specified in AS/NZS 1269.4, 2005. Where ambient noise is greater than this, noise-excluding head sets or a testing booth should be used. Ideally, audiograms should be performed in specially designed booths which enable some individuals to detect sounds at the threshold of hearing.

5. Technical equipment should meet accepted standards and be calibrated regularly.

The Diagnosis of NIHL

DOL [in common with international practice] has adopted pure tone measurements to diagnose NIHL.

This may not reflect a person’s ability to communicate in a workplace – which is often the most serious effect of NIHL.

The following criteria have been chosen to make the diagnosis as straight-forward and reproducible as possible.

Occupational History

There should be a clear history of sustained exposure to loud noise at work. The practitioner should ask the person what industries they have worked in and for how long in each industry. An attempt to identify the approximate noise levels at each task (e.g. was speech possible without shouting? were the ears ringing at the end of the day or week?) should be made and the control measures employed (hearing protection, engineering control, hearing surveillance) should be assessed. Comment should be made concerning the degree and type of recreational noise exposure.

Results of the screening audiogram

Audiometry should not be a stand-alone function but be part of an industry-based hearing conservation programme. In order to make the diagnosis of NIHL, the following are necessary:

1. The shape of the hearing threshold curve should show a characteristic notch at 4-6 kHz, with a recovery at high frequencies usually required. A normal audiogram is shown in Fig. 1. This is contrasted with a “typical” noise induced hearing loss audiogram shown in Fig. 2.

(Because an audiogram does not match this pattern, a noise-induced hearing loss cannot be excluded. As the NIHL increases, the notch widens and is lost.

AUDIOGRAMS

Figure 1 – Normal Audiogram

Figure 2 – Noise induced hearing loss

2. A symmetrical loss is expected in each ear, or there should be an explanation for asymmetry. Asymmetry could result from a hobby involving rifle shooting. If there is no convincing explanation for asymmetrical loss, referral to an otolaryngologist should be considered.

3. For the purposes of notification to the NODS, the audiogram must measure the magnitude of the hearing loss by noting the depth of the notch from an established baseline.

The criteria adopted for notification is that the threshold at 4KHz is at least 30dB Hearing Loss (HL) and is at least 15dB worse than the 2KHz threshold.

Loss of Recovery above 6kHz

It is usual for the audiogram to show a recovery in both ears for frequencies above 6 kHz. If this recovery is not present, the diagnosis of NIHL should be reconsidered. Many severe cases of NIHL do not show this recovery (sometimes this recovery is absent because of tinnitus) and NODS will accept a case without high-frequency recovery, accompanied by an explanatory note by a referring or reviewing specialist.

Notification

The Department of Labour will accept notification without further validation from otolaryngologists, occupational physicians or other health professionals who have undertaken and passed the National Audiology Centre’s 2-day hearing conservation introductory course.

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Biological Exposure Indices

Biological monitoring — the measurement of a substance (or its metabolites) in body fluids such as urine or blood — provides a complementary approach to air monitoring for the estimation of exposure to workplace contaminants.

A Biological exposure index (BEI) is defined as follows:

• If a worker’s inhalation exposure is equal to the WES, and he/she is engaged in moderate work, then the BEI represents the expected level of the biological determinant.

In most cases, the BEI has been derived from the observed relationship between the measured exposure and the biological level, but in some instances the relationship between the biological level and the potential health effects has been approached more directly.

Results from biological determination may reflect:

• very recent acute exposure
• the average exposure over the last few day(s), or
• long-term cumulative exposure.

The BEIs assume that the exposure has been reasonably steady and that an 8-hour day, 5-day week has been worked. Extrapolation to other exposures can be made but only with a clear under-standing of the relationship between the absorption, metabolism, and elimination of the substance in question.

Biological monitoring has been widely used to monitor the uptake of cumulative toxins (e.g. lead, mercury, organophosphate insecticides).

It also may be employed effectively where there is a significant potential for increased uptake as a result of skin absorption, increased respiratory rate, or exposure outside of the workplace.

Generally a BEI associated with only one assay is given for exposure to each substance, even though there may be several possible ways of estimating exposure. Preference has been given to urinary assays over more invasive blood tests but factors such as the stability of the sample and the possibility of interferences have also been considered.

For routine surveillance of exposure to some substances, biological monitoring may be preferred over air sampling. E.g: if the substance has a long half-life in the body, the monitoring will give a result that reflects an integrated exposure. Or the equivalent air sampling procedure may, because of the typical work practices or sampling difficulties encountered, give less reliable results.

Quantitative interpretation of biological monitoring results is often difficult. The quality of the information may be improved if the measurements obtained from several workers with similar exposure, or serial determinations on an individual worker, are considered. Before doing biological monitoring, it is essential to get background information, including data on the pharmacokinetics of the substance, interferences, and background levels of the determinant.

BEIs exist for:

• Acetone
• Arsenic
• cadmium
• carbon monoxide
• chromium
• Cobalt
• 2-ethoxyethanol
• Fluorides
• hexane
• Lead
• mercury
• pentachlorophenol
• Phenol
• Styrene
• trichloroethylene
• methyl alcohol
• methyl ethyl ketone (MEK)
• methyl isobutyl ketone (MIBK)
• organophosphates
• sodium fluoro-acetate (1080)
• Xylene

Canterbury Health Laboratories have a comprehensive booklet on the methods for taking samples. Contact: www.cdhb.govt.nz/chlabs.

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