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Local exhaust ventilation

Contents

  1. Introduction
  2. Maintenance
  3. Safety and health representatives
  4. Regulations
  5. The system has five major parts
  6. Legislation

1. Introduction

Local exhaust ventilation captures air contaminants at their source.

It is necessary when:

  • the contaminant is harmful, toxic or corrosive (such as lead fumes, acid mist, solvent vapour);
  • contaminant levels are high;
  • contaminants must be filtered out before release into the air; or
  • the process gives off heat.

It is most effective because:

  • it minimises employee exposure to contaminants;
  • the volume of exhaust air is much less than for general ventilation;
  • the contaminant can be collected for disposal or recovery;
  • equipment in the workplace is protected from heat and corrosive substances; and
  • employees may not have to wear respiratory protection.

2. Maintenance

Maintenance and cleaning are vital to the efficiency of local exhaust ventilation systems. Easy access for cleaning and removing captured contaminants and test points to carry out checks are both important considerations when installing a system.

Whatever ventilation system you choose, it must be capable of capturing the maximum surge of contaminants.

3. Safety and health representatives

The Act entitles employees to elect safety and health representatives to represent and inform them on issues involving their safety and health, to consult with employers on resolving these issues and to assist in their resolution.

4. Regulations

Regulation 5.20 of the Occupational Safety and Health Regulations 1996 requires that, as far as practicable, employers must reduced the risks from hazardous substances. The regulation also requires that control measures such as ventilation be used in preference to personal protective equipment.

5. The system has five major parts

The Hood

Hoods come in a variety of designs. The one you choose should enclose or be located as close as possible to the contaminant source and be matched to the particular process. The hood should be designed so it captures contaminants as they are given off.

The Ducts

Ducts carry the contaminants from the capture point to an outlet point. Air velocity in the ducting must be high enough to prevent contaminants settling in the system, but not so high that it causes vibration and noise problems. To ensure the correct balance is obtained, consult an Occupational Hygienist or Ventilation Engineer.

The Fan

the heart of the system, creating movement of air to shift the contaminants. Centrifugal fans are generally best for high pressures, and axial fans are best for low pressure/high volume applications.

Filters

Filtering equipment captures contaminants in the extracted air and lets clean air continue through. The filtering equipment you install will depend on the type and volume of contaminants.

Discharge Stack

The discharge stack releases exhaust gas into the air. It must be high enough to avoid gas re-entering the workplace and make sure contaminant levels on the ground are within clean air standards. Stacks should be at least two metres above the highest roof or adjacent building and away from air inlets. Weather caps aren't a good idea as they can hinder vertical discharge. The Department of Environmental Protection requires a minimum air velocity discharge of six metres a second.

6. Legislation

The Occupational Safety and Health Act 1984 requires employers to provide employees with a safe and healthy work environment, and employees to take reasonable care with their own safety and health and the safety and health of others at work.

An employer shall:

  • ensure employees are not exposed to workplace safety and health hazards;
  • provide employees with adequate information, instruction and training;
  • consult with safety and health representatives and other employees about workplace safety and health; and
  • where it is impracticable to prevent exposure to hazards, provide employees with adequate personal protective clothing and equipment.

Employees shall:

  • take reasonable care of their own health and the health of others; and
  • co-operate with employers in carrying out safety and health requirements.

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