Module 1: Occupational Hygiene - Section 3: Evaluation of Airborne Contaminants
OH3.1: Introduction
 

GENERAL OBJECTIVES
Introduce students to techniques that are used to evaluate workers' exposure to harmful chemical substances.

SPECIFIC OBJECTIVES
After completing this Module students are expected to be able to:
  • understand the principles involved in deciding on a sampling medium
  • design a sampling strategy aimed at evaluating a specific contaminant
  • be familiar with the various equipment items that are used to collect air samples; and
  • recommend an analytical technique based on the nature of contaminant being evaluated
  • calculate concentration of the contaminant and to compare it with applicable standards.

INTRODUCTION:

In terms of the Regulation for Hazardous Chemical Substances, if an employee is significantly exposed to a hazardous substance the employer is obliged to initiate an evaluation programme. The goals of such an evaluation programme would be to measure the extent of exposure and to assess impact of exposure on the health of employees.

There are three approaches that can be used to evaluate worker's exposure to airborne chemical contaminants, namely, environmental monitoring, biological monitoring and medical surveillance. Environmental monitoring indicates presence or not of airborne contaminants; biological monitoring documents absorption of contaminants into the body; and medical surveillance is used to detect adverse health effects (including biological effect monitoring) which may be due to exposure. The focus of this module is on environmental monitoring and biological monitoring will be discussed briefly. Medical surveillance is dealt with in the Modules on Occupational Medicine later in the course.

ENVIRONMENTAL MONITORING:

Environmental monitoring assesses the level of airborne contaminants in the workplace atmosphere. This is achieved by sampling a known volume of air into a sampling medium which is then sent to a laboratory for analysis. Sampling and analysis are complementary activities. Analytical sensitivity governs the minimum volume of air to be sampled, and the choice of medium for capturing air contaminants is partly governed by its suitability for the subsequent analysis.

What is air sampling?

Air sampling is taking a known volume of air through a sampling medium (normally a filter paper for solids and a sorbent tube or glass impinger for gases) on or in which the contaminant is captured. The concentration of the contaminant is calculated using the volume of air and the amount of pollutant captured. Standardised air sampling and analytical methods have been developed to ensure accurate and meaningful information is collected.

Why air sampling?

Air is sampled for the following reasons:

REFERENCES:



Todd LA. Evaluation of the Work Environment. In: Encyclopaedia of Occupational Health and Safety. http://www.ilo.org/safework_bookshelf/english/

American Conference of Governmental Industrial Hygienists. Air Sampling Instruments for Evaluation of Atmospheric Contaminants. 8th Edition 1995.

Pepper A and Evans G. Occupational Exposure Limits; Principles of Air Sampling; Particle Behaviour. In: Human Response, Standards, Sampling. NEBOSH Diploma Module C. Published by University of Portsmouth, 1992.

Hazardous Chemical Substances Regulations, 1995 (Extract)

Section 6. Air monitoring:
  1. Where the inhalation of an HCS is concerned, an employer contemplated in regulation 5(4) shall ensure that the measurement programme of the airborne concentrations of the HCS to which an employee is exposed, is:

    a. carried out in accordance with the provisions of these regulations;

    b. carried out only after the relevant health and safety representative or relevant health and safety committee has been informed thereof and given a reasonable opportunity to comment thereon;

    c. carried out by an approved inspection authority or by a person whose ability to do the measurements is verified by an approved inspection authority;

    d. representative of the exposure of employees to the airborne HCS in accordance with the provisions of subregulation (2); and

    e. verified in accordance with the provisions of subregulation (3) if the measurements are carried out by a person who is not an approved inspection authority.

  2. In order to comply with the provisions of subregulation (1).(d) an employer shall;

    a. ensure that the measurement programme, in the case of a group measurement, makes provision for the selection of the number of persons for a sample to be done as contemplated in chapters 3 and 4 and Technical Appendix A of the OESSM: Provided that such sample size shall be chosen for the top 10% of the group at the 95% confidence level for an HCS with a control limit and for the top 10% of the group at the 90% confidence level for an HCS with a recommended limit; and

    b. carry out the representative measurements at least every 12 months for an HCS with a control limit and at least every 24 months for an HCS with a recommended limit: Provided that whenever the control limit or recommended limit which has been prescribed for an HCS is exceeded, the provisions of regulation 10 shall apply.

  3. In order to comply with the provisions of subregulation (1).(e), an employer shall obtain the service of an approved inspection authority who shall, at intervals not exceeding 24 months:

    a. verify, by examining the measurement and analysis equipment of the employer and questioning the person referred to in subregulation (1).(c), regarding the carrying out of the measurement programme;

    b. carry out the measurements prescribed by subregulations (1) and (2) for any one group; and

    c. enter the results of the investigation and measurements as contemplated in paragraphs (a) and (b) respectively in the record required by regulation 9.

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General Introduction to Occupational Health: Occupational Hygiene, Epidemiology & Biostatistics by Prof Jonny Myers is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License
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