Local Exhaust Ventilation (LEV) System Testing & Examination

A local exhaust ventilation system is a type of engineering control equipment commonly used in workplaces to manage exposure to chemicals hazardous to health. The Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations 2000 specify requirements for the design, commissioning, inspection, and testing of local exhaust ventilation systems.

The effectiveness and efficiency of these systems depend on their design, proper usage, and regular maintenance. Therefore, it is mandatory for the local exhaust ventilation system to be inspected with a proper inspection record at least once a month.

Additionally, it must be examined and tested at least once every 12 months (or at shorter interval as specified by the designer) by a registered hygiene technician as outlined by the Guidelines on Occupational Safety and Health for Design, Inspection, Testing and Examination of Local Exhaust Ventilation System.

This ensures that the risks associated with the use of chemicals hazardous to health are efficiently controlled through the use of the local exhaust ventilation system.

What is a Local Exhaust Ventilation (LEV) System?

A Local Exhaust Ventilation (LEV) system is a widely used form of engineering control equipment designed to protect employees from exposure to hazardous chemicals in the workplace. As a crucial component of engineering controls, LEV systems play an integral role in chemical health risk assessments (CHRA) and chemical exposure monitoring (CEM).

It operates on the principle of capturing airborne contaminants at or near their source, preventing them from dispersing into the work environment. These contaminants may include dust, smoke, mist, aerosol, vapor, and gas.

A basic schematic diagram of a local exhaust ventilation system. Image inspired from worksafe.gov.nz.

Key Components of a Local Exhaust Ventilation System
An LEV system typically consists of four main components: the hood, duct system, air cleaner, and fan. Each component plays a vital role in the system’s overall effectiveness:

a) Hood
The hood is the most critical component of the LEV system. Its primary function is to collect airborne contaminants by directing the contaminated air stream towards the hood.

The efficiency of an LEV system largely depends on the hood’s ability to capture contaminants, ensuring that their concentration in the workroom remains below acceptable limits. Hoods can be categorized into two types:

  1. Enclosure Hood
    This type of hood surrounds the source of contamination as much as possible, using walls and doors with minimal openings. In some cases, it may completely enclose the contaminant source. Examples include fume booths, asbestos debagging booths, and spray painting booths.
  2. Exterior Hood
    Exterior hoods are designed to capture contaminants from outside the source area. They are located adjacent to the contamination source rather than enclosing it. Examples include side hoods, slot hoods, downdraft hoods, push-pull system hoods, low-volume and high-velocity hoods, and canopy hoods.

b) Ducting System
The ducting system consists of a network of ducts that connect the hood to other components of the LEV system. It transports contaminated air to the air cleaner. The duct on the fan outlet typically discharges air to the atmosphere.

Designing the ducting system to minimize energy losses is crucial to maintaining proper airflow, as reduced flow can cause dust accumulation, leading to blockages and decreased suction efficiency at the hood.

c) Air Cleaner
The air cleaner is responsible for removing contaminants from the air collected by the hood. This is essential to prevent harmful substances from being discharged into the community environment or to recover materials with salvage value.

Air cleaners are also used to purify exhaust air before it is re-circulated back into the workplace. Common types of air cleaners include filter bags, cyclones, and wet scrubbers.

d) Fan
The fan serves as the system’s air-moving device, providing the necessary energy to draw air and contaminants into the hood by creating negative pressure or suction in the ducts. It converts electrical power or other forms of energy into negative pressure, increasing air velocity.

The fan must overcome various losses, including friction, hood entry, ducting system, and air cleaner losses, while ensuring the required airflow rate to extract and transport contaminated air effectively.

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How is Local Exhaust Ventilation System Testing & Examination Conducted?

The local exhaust ventilation system testing and examination is conducted in accordance with the principles outlined in the guidelines established by the Department of Occupational Safety and Health (DOSH), specifically the “Guidelines on Occupational Safety and Health for Design, Inspection, Testing and Examination of Local Exhaust Ventilation System.”

Below are the steps or methodologies taken during the assessment.

Before conducting the examination and testing, we will require information on your LEV unit to be assessed such as:

  1. Location and placement of the unit
  2. Size of the LEV unit
  3. Total number of LEV unit
  4. Copy of previous testing report (if available)
  5. Copy of CHRA report (if available)

During the inspection, testing, and examination of local exhaust ventilation systems, the following precautionary measures should be implemented:

a) Inspect, Test, and Examine Inside of Ducts
Implement measures to prevent chemical poisoning or exposure to chemical hazards while inspecting the interior of ducts.

b) Inspect, Test, and Examine Motors
Implement measures to avoid contact with dangerous parts of the motor that could cause injury during inspection, testing, and examination.

c) Inspect, Test, and Examine Passages and Scaffolds
Implement measures to prevent slips or falls during the inspection, testing, and examination of passages and scaffolds.

d) Inspect, Test, and Examine Electrical Parts
Implement measures to prevent electrical shock during the inspection, testing, and examination of electrical components.

The worksite where the local exhaust ventilation (LEV) system is located must be thoroughly prepared to ensure that our hygiene technicians are not exposed to any hazards during testing and inspection activities.

You should ensure that all access points to the LEV unit are secure and safe for use by our hygiene technicians. For instance, if the LEV unit requires access to an elevated working platform, you must provide suitable means of access, such as a ladder, lift, scaffolding, crane, or any other necessary equipment.

a) Hood
At the hood unit, the inspection, examination and testing of following items will be conducted:

  1. Physical appearance of the hood
  2. Obstruction of flow
  3. Direction and size of opening area for exterior hoods
  4. Velocity
  5. Environmental monitoring
  6. Hood static pressure

b) Duct
At the duct unit, the inspection, examination and testing of following items will be conducted:

  1. Physical condition of duct outer surface
  2. Physical condition of duct inner surface
  3. Loose joints
  4. Condition of inspection holes
  5. Static pressure
  6. Duct velocity
  7. Temperature in the duct

c) Damper
At the damper unit, the inspection, examination and testing of following items will be conducted:

  1. Condition of the damper
  2. Static pressure

d) Fan
At the fan unit, the inspection, examination and testing of following items will be conducted:

  1. Condition of outer casing surface
  2. Condition of inner surface of casings, impellers, and guide vanes
  3. Condition of belts, etc.
  4. Rotating direction of fan
  5. Condition of bearings

e) Air Cleaner
At the air cleaner unit, the inspection, examination and testing of following items will be conducted:

  1. Physical appearance
  2. Static pressure

After collecting the data, our hygiene technician will analyze it and prepare the report within 30 days. Once the final report is presented and agreed upon, a copy will be provided to your organization for record-keeping.

An illustration of a laboratory employee working near a local exhaust ventilation system.

What are Included in the Local Exhaust Ventilation System Testing & Examination Report?

The local exhaust ventilation system testing and examination report will be divided into several main sections, each containing core elements essential to the assessment as per outlined below.

The front page of the report should serve as the title page and will contain the following information:

  1. The title of the report, e.g., “Report of Local Exhaust Ventilation System Testing & Examination at Laboratory A 2023“
  2. Assigned report reference number, including assessor registration number, year of assessment, and serial number. Example: “Report Reference Number: HQ/23/ASS/00/00002-2023/001”
  3. Assessor’s Name and Competency Registration Number
  4. Company’s Name, Registration of Company Number (ROC), and DOSH Registration Number (where applicable)
  5. Premise address where LEV system testing and examination is conducted

The section provides a comprehensive overview of the inspection, testing, and examination of Local Exhaust Ventilation (LEV) systems, which are crucial for controlling exposure to hazardous chemicals in industrial environments.

The summary also includes a concise overview of the results, noting the physical condition and performance of the system’s components, such as hoods, ducts, air cleaners, and fans, and provides recommendations for improvements or maintenance.

The section describes the system’s components, such as exhaust hoods, ducting, air cleaning devices, and exhaust fans, and highlights their roles in ensuring the system’s overall effectiveness.

Additionally, it outlines the initial evaluation process, which assesses the system’s ability to protect workers by keeping exposure levels below permissible limits and verifying the operational parameters, such as duct velocity and fan speed.

The section lists all the relevant objectives of the local exhaust ventilation system testing and examination.

The process information section offers a detailed description of the industrial setting and the specific LEV systems tested and inspected. It outlines the different types of hoods used, the nature of the contaminants present, and the frequency of inspections conducted.

It also provides context for understanding how the LEV systems are integrated into the workplace to manage hazardous emissions effectively.

The methodology section details the instruments and materials used during the inspection and testing of the LEV systems, such as measuring tapes, Pitot tubes, hot wire anemometers, and manometers. It describes the inspection process, which includes checking the physical condition of all components, conducting smoke tests, identifying obstructions to airflow, and maintaining equipment like fans and motors.

Additionally, it also outlines the testing and examination procedures, to assess aspects like capture velocity, static pressure, duct transport velocity, and fan efficiency.

This section summarizes the outcomes of the LEV system testing, highlighting the performance of various components, including hood face velocity and duct transport velocity.

The results are compared with the ACGIH’s recommended values and design specifications to identify any discrepancies or areas needing improvement. The analysis provides insight into the overall effectiveness of the LEV systems in controlling hazardous emissions.

The discussion section delves into the LEV systems’ effectiveness in managing contaminants, noting any deficiencies or issues discovered during testing. It offers a detailed analysis of the performance of specific components, such as hoods, ducts, fans, and chimneys, and evaluates their impact on the system’s efficiency.

It also emphasizes the importance of addressing any identified issues to maintain optimal system performance.

This section provides recommendations based on the hierarchy of control, which is a systematic approach to managing workplace hazards. The hierarchy consists of several levels of control measures, each designed to reduce or eliminate risks associated with exposure to hazardous substances in industrial environments.

The recommendations may include elimination, substitution, engineering controls, administrative controls, and personal protective equipment (PPE).

The conclusion section reaffirms that the LEV systems have been successfully inspected and examined, with effective face velocities and duct transport velocities observed in most instances. It notes specific issues, if any.

The conclusion also cautions against neglecting internal maintenance, which could lead to system deterioration over time.

What are the Benefits of LEV System Testing & Examination to the Organization

1. Ensures Compliance with Regulations
Conducting regular testing and examination of LEV systems ensures compliance with occupational safety and health regulations, such as the Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations 2000. This compliance is crucial for meeting legal requirements and maintaining a safe working environment.

2. Enhances System Efficiency
Regular inspection and testing of LEV systems help verify that all components, such as hoods, ducts, air cleaners, and fans, are functioning correctly.

This ensures that the systems operate at optimal efficiency, effectively capturing and removing airborne contaminants from the workplace. Improved system efficiency minimizes the risk of exposure to hazardous chemicals for employees.

3. Identifies and Mitigates Potential Hazards
Testing and examination of LEV systems allow for the identification of physical defects or inefficiencies, such as blockages, leaks, or insufficient air velocity. By addressing these issues promptly, employers can mitigate potential hazards, preventing health risks and ensuring a safer work environment for employees.

4. Prolongs Equipment Lifespan
Routine maintenance and testing of LEV systems can prevent wear and tear, ensuring that components such as fans, motors, and ducts remain in good working condition. This proactive approach extends the lifespan of the equipment, reducing the need for costly repairs or replacements and maintaining consistent system performance.

5. Supports Continuous Improvement
The data collected from LEV system testing and examination provide valuable insights into the system’s performance over time. This information can inform continuous improvement efforts, allowing employers to make informed decisions about system upgrades, enhancements, or modifications.

Regular evaluations also promote a culture of safety and accountability, encouraging ongoing efforts to optimize workplace safety practices.

LEV System Testing & Examination Frequently Asked Questions (FAQ)

According to the Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations 2000, LEV systems should be inspected at appropriate intervals, with inspections occurring at least every month and a thorough examination and testing conducted at least once every 12 months by a qualified hygiene technician. These intervals may vary based on specific system requirements and manufacturer recommendations.

Key components of an LEV system that require regular inspection and maintenance include hoods, ducts, air cleaning devices, and exhaust fans. Each component plays a crucial role in the system’s overall effectiveness.

Regular checks ensure there are no physical defects, blockages, or inefficiencies that could compromise the system’s performance in capturing and removing contaminants.

No, the monthly inspection of Local Exhaust Ventilation (LEV) systems does not need to be conducted by a registered hygiene technician. While a hygiene technician must perform the annual examination and testing to assess the system’s effectiveness, the monthly inspections can be carried out by any competent person who has been trained in the procedures.

These inspections focus on identifying obvious physical defects, obstructions, or operational issues to ensure the system remains in good working order until the next formal examination.

Conducting a monthly inspection of Local Exhaust Ventilation (LEV) systems involves a systematic approach to ensure that all components function effectively and efficiently. Here are the key steps to follow:

Visual Inspection of Components

  1. Hoods – Check for physical damage, such as corrosion, dents, or obstructions that might affect airflow. Ensure that contaminants are being captured effectively.
  2. Ducts – Inspect for any signs of physical damage, blockages, or leaks. Ensure that all connections are secure and that there are no abnormal noises or vibrations.
  3. Air Cleaners – Check for any damage or wear, and ensure that filters are not clogged or in need of replacement.
  4. Fans – Inspect the fan blades for wear and tear, check for excessive noise or vibration, and verify that the fan is operating in the correct direction.

Functional Testing

  1. Airflow Measurements – Use an anemometer or similar device to measure the face velocity at the hood openings. Compare these measurements against recommended standards to ensure adequate airflow.
  2. Pressure Readings – Measure static and velocity pressure within the ducts using a manometer to confirm that the system maintains proper airflow dynamics.

Smoke Testing

Conduct a smoke test to visualize airflow patterns and verify that contaminants are being captured and exhausted properly. This can help identify any areas where airflow may be insufficient.

Documentation

Maintain detailed records of all findings, including any defects or maintenance issues identified during the inspection. Use a checklist to ensure all areas are covered and keep a log of inspection dates and outcomes for compliance purposes.

Corrective Actions

Address any issues identified during the inspection promptly. This may involve cleaning ducts, repairing or replacing damaged components, or adjusting system settings to optimize performance.

References

  1. Occupational Safety and Health Act (OSHA) 1994.
  2. Occupational Safety and Health (Use and Standards of Exposure of Chemicals Hazardous to Health) Regulations, 2000.
  3. Guidelines on Occupational Safety and Health for Design, Inspection, Testing and Examination of Local Exhaust Ventilation System.