Monitoring solvent vapour levels

How operatives can be protected against a particular hazard encountered in many factories.

Organic solvents are incredibly versatile chemicals which can be used in a wide variety of industries. This may mean that workers are exposed to these substances on a daily basis in their place of employment. Many applications – for example, as adhesives, primers, cleaners, degreasers, inks and finishing agents – involve formulations and preparations containing organic solvents. The measurement of airborne solvent vapour concentrations may be required for a number of reasons, including:

• to help assess possible health risks resulting from work activities
• to assess the effect of changes in materials, procedures or controls
• to determine compliance with ‘workplace exposure limits’ (WELs)
• to identify the need for, and the effectiveness of, exposure control measures
• to reassure members of staff who may be exposed to solvents
• to comply with specific legal requirements.

Within the United Kingdom, various legislation and guidance from the Health and Safety Executive (HSE) help to control employees’ exposure to harmful chemicals in the workplace. This can involve monitoring of exposure to these substances. Several techniques and equipment are available for measuring solvent vapour concentrations. They can all help in the assessment and control of exposure to solvent vapours in the workplace, but it is essential that the appropriate monitoring technique is selected. More importantly, the results should be analysed and interpreted correctly by competent personnel. This is necessary because measurements may form the basis of decisions on possible health risks, compliance with regulations and investment in control measures.

Effects on human health

Solvents can enter the human body by three routes of exposure: inhalation, ingestion or skin absorption. Some organic solvents are volatile and will readily form a vapour in air at relatively low temperatures. If the use of solvents is not controlled, this vapour can cause both short-term (acute) and long-term (chronic) health problems.

Typical effects of a short-term exposure to solvent vapour include headaches, dizziness, nausea and contact dermatitis. In extreme cases, exposure to very high concentrations of solvents has proved fatal.

Control measures

Many national health and safety regulations will include requirements to keep exposure to hazardous substances within ‘acceptable’ limits. In some cases, there is also a requirement to reduce exposure ‘as far as is reasonably practicable’ – that is to say, where the cost of adding additional control measures are reasonable relative to the risk reduction, they should be implemented. The effective control of solvent vapour releases can also have cost-saving benefits, such as reducing solvent usage and wastage, and by reducing waste disposal costs.

COSHH

The HSE is responsible for the safety of workers in the UK. This includes the publishing and implementation of regulations to ensure and improve the safety of working environments. The Control of Substances Hazardous to Health Regulations 2002 (COSHH) states that where substances are known to be carcinogenic, mutagenic or asthmagens, exposure must be controlled to be as low as is reasonably practicable (ALARP).

According to this publication, a substance can be taken into the body by:

• breathing in fumes, dust, gas or mist
• skin contact
• injection into the skin
• swallowing.

WELs are occupational exposure limits based on either a long-term (eight-hour) or short-term (15-minute) exposure period for specific substances that have been approved by the HSE to protect the health of employees. WEL limits are identified in a database entitled ‘EH40/2005 Workplace exposure limits (as amended)’. Specific limits are identified within this document for individual substances. For example, ethanol (CAS 64-17-5) has an eight-hour exposure limit of 1,000 parts per million (ppm).

What to measure

As the results of measurements may form the basis of significant decisions on possible health risks, regulatory compliance and investment in suitable control measures, it is important that they are undertaken in a structured manner and that the technique used is appropriate for the process being monitored.

Average concentration level measurements are particularly useful for measuring personal exposure by sampling air from the working environment. This type of monitoring typically involves the use of solvent vapour monitoring badges.

To demonstrate that exposure levels are not being exceeded, the sample collected, measured or analysed should be representative of the workplace atmosphere. This will provide the best indication of the type of control measures or compliance actions necessary to be most effective relative to the application. Several factors need to be considered prior to selecting an air monitoring technique:

• specificity – the ability to uniquely detect one solvent in the presence of other contaminants
• accuracy – how close the results are to the actual concentration present
• sensitivity – the concentration of solvent that must be present to obtain a result
• cost – the expense associated with the purchase of equipment or supplies, as well as any associated laboratory analysis costs
• ease of use – if specific training is required to accurately conduct the test, and how difficult it is to operate the equipment
• calibration – checks are required to verify that the detection technique is performing accurately at the relevant concentration levels.

Solvent vapour levels

Once specific needs have been assessed, and if it has been decided that solvent vapour badge monitoring is the most appropriate method, SATRA can offer a full range of technical services. Solvent vapour monitoring badges can be supplied by SATRA and are designed to be worn by individual operatives who are exposed to solvent vapours during the course of their work.

The badges are attached to clothing at the front of the upper body for the duration of the work period. The badges absorb the solvent vapours during a representative typical work period and can be returned to SATRA’s chemical laboratory for analysis. Analysis of the vapour badges is conducted in accordance with EN ISO 16200-2:2000 by Gas Chromatography with Mass Spectrometry (GC-MS) liquid injection. The solvents (and their WELs) that are able to be analysed at SATRA are listed in table 1. Additional solvents can be added to this analysis if required.

Table 1: Analytes and WEL limits for long-term (eight-hour) exposure
Solvent	WEL (ppm)
Acetone	500
2-Butanone (MEK)	200
n-Butyl acetate	150
Cyclohexanone	10
Dichloromethane	100
Dimethylformamide	5
Ethanol	1,000
Ethyl acetate	200
Ethylbenzene	100
n-Hexane	20
Propan-2-ol (IPA)	400
Styrene	100
Tetrahydrofuran	50
Toluene	50
m-Xylene	50
o-Xylene	50
p-Xylene	50

Interpreting results

All work activities should be subject to a periodic risk assessment which aims to identify hazards and confirm that appropriate control measures are in place. Where solvents are involved, the measurement of vapour levels may be necessary as part of an overall risk management strategy.

The results obtained should be supported by and interpreted in light of other information. This will include the presence and performance of ventilation systems, observations of work procedures, views and opinions of those conducting the work, and benchmarking against custom and practice within the industry.

Consideration of the results of exposure measurements should identify if immediate action is necessary to eliminate or reduce exposure, as well as if a programme of planned improvements or more detailed measurements are required.

Solvent monitoring results should become part of a recognised health and safety management system. The results can be used to demonstrate good practice and to plan, measure and review health and safety issues within the workplace.

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