BOHS P601 Thorough Examination & Testing of Local Exhaust Ventilation (LEV) Systems

BOHS P601 Thorough Examination & Testing of Local Exhaust Ventilation (LEV) Systems

Safety Training

BOHS P601 Thorough Examination & Testing of Local Exhaust Ventilation (LEV) Systems

Course Date(s)

5 day course
18th 19th 20th 21st 22nd Nov

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P601 - Thorough Examination and Testing of Local
Exhaust Ventilation Systems

To provide the methodology, theoretical and practical knowledge to enable candidates to:
* Understand the principles of good control practice for hazardous substances and the role of local exhaust ventilation (LEV) in this regard.
* Carry out the testing of previously appraised LEV systems used to control exposure to substances hazardous to health.
* Produce suitable records of the results of examination and testing as required by regulatory guidance and codes of practice.
* Understand and be able to describe the principles and the main elements of an LEV system.
* Judge whether an LEV system is capable of adequate control of the identified hazards.
* Carry out the necessary measurements safely to determine if an LEV system is effective and operating to the design specification.
* Establish, in circumstances where a system has not been properly commissioned, whether the system works effectively, controls exposure and also determine the operating criteria for continued performance.
* Provide suitable advice to remedy any faults discovered.

Prior Knowledge
Candidates are expected to have a basic knowledge of the components of ventilation systems and their functions, and to be familiar with the contents of HSG258 Controlling airborne contaminants at work:

Course Content:


The syllabus is structured into four sections

Educational Objectives

Candidates should gain an understanding of the complex nature of exposures in the workplace, appreciate the basic principles of workplace control and the type of approach that is

required for successful implementation of a control programme. Candidates should be able to relate the outcome of a risk assessment to selection of control options.

1. Principles of Good Control Practice

How hazards and risks are identified in the workplace.
The range, reliability and effectiveness of control options including work procedures, process engineering controls, ventilation and PPE.

Practicable programmes for control which may involve a combination of measures.
Practical application of the use of a combination of measures including a stepwise approach to their implementation.
The identification of effective control strategies as they relate to reasonable practicability.
The control of emissions as they relate to the control of exposure.
Achieving Control
The meaning of adequate control including reference to WELs and other published or in-house standards.
Duties under the COSHH Regulations, the Control of Lead at Work Regulations and the Control of Asbestos Regulations 2012.
The Role of Risk Assessment
Identifying exposures.
Confirming compliance.
Achieving adequate control at the design stage and in existing facilities from normal operations and during non-routine or maintenance activities.
Ventilation Systems and their Performance Evaluation (50%)


Educational Objectives
Candidates should gain a basic understanding of the principles of the design of ventilation systems and the differences between general and local exhaust systems in terms of application and performance. Candidates should be able to carry out the appropriate measurements to check the effectiveness of the ventilation system and be able to identify when air sampling is required to determine whether adequate control is being achieved. In circumstances where an existing system has not been commissioned properly, candidates should be able to carry out appropriate measurements to assess the effectiveness of such a system and document the results.

2. Types of System

Ventilation systems in the workplace.
Local exhaust ventilation.
Principles of Ventilation Systems and their Components
Basic design principles of the system itself and of its components, including: hood designs, (enclosures, captor hoods, booths, partial enclosures and receptor hoods), ducts, fans, air cleaners and discharge arrangements. Special types of ventilation system including push-pull systems, High Velocity Low Volume (HVLV) systems etc.
Application of hoods, slots, enclosures to industrial situations. Definition of capture velocity and face velocity.
The importance of air distribution across the face of a large extract hood.
Ducts and transport velocities; duct size, configuration and materials.
Fans (types and their application, effects of direction of rotation).
Air cleaners, treatment systems and filtration standards (types and their performance, for example gravity and centrifugal collectors, dry fabric, electrostatic, wet methods, absorption).
Facilities for maintenance, examination, testing and conditioning.
Balancing of air flows within systems and with the immediate environment.
The nature of flammable dusts and vapours and of explosion prevention, and explosion relief in relation to LEV.
Discharge arrangements and the risk of recirculation of contaminated air, including inadvertent contamination of air intakes by discharged air.
General Ventilation Systems

Use of general ventilation systems as a means of controlling exposures.
Principles of natural ventilation and infiltration.
Mechanical ventilation, dilution or displacement, including methods of delivery and distribution.
How hot plumes behave.
Determination and calculation of ventilation requirements.
Application and limitations of general ventilation.
Measurement and Testing of LEV Systems
Performance considerations:
The measurement of performance and its relation to the attainment of control of exposure including limitations of measurement equipment and the need for calibration. Determining whether all of the significant sources of exposure are capable of being controlled adequately.
Qualitative assessment of systems. The visualisation of air flows and their effective capture of the contaminant(s) into the ventilation system which must include the use of a dust lamps, smoke generators and/or smoke tubes.
The operation of pressure and flow measurement instrumentation, including Pitot tubes and micro-manometers, anemometers [thermal and vane] etc. to provide quantitative data on ventilation systems. Appropriate locations of test points to take such measurements.
Full understanding of all calculations for volume flows from pressure and velocity measurements.
The requirements, including frequency, for maintenance examination and test; periodic checks and inspections, thorough examinations, statutory examinations and testing. A suitable reporting scheme for results is also required.
The requirements for commissioning an existing system that does not have any suitable commissioning documentation.
The specification of suitable measurable performance criteria for an LEV system.
The effects of partial or total blockages in a section of duct, the effects of filter blinding, holes in filter bags, air by-passing the filters etc.
Test procedures and standards of air re-circulation system.
Practicability of the system for use and limitations of LEV.

3  Health and Safety During Examination and Testing of LEV Systems
Educational Objectives
Candidates must be able to make an assessment of all relevant risks, both to their own safety, and how their actions might possibly affect the safety of others as related to ventilation system.
Understand the basic requirements for personal protection including respiratory protective equipment for individual protection during evaluation of operating ventilation systems.

Additionally candidates should be aware of:

Need to comply with permit to work systems and lock-out procedures.
Safety aspects of working at heights, use of ladders, cherry-picker etc, (avoidance of dropping things on people below them).
The effect of a hot plume of contaminated air (if the extract to be tested is high up).
The potential effect of testing on the discharge side of the fan (contaminated air blowing out under a positive pressure).
The potential consequences of any actions they might take to correct the performance of a system (eg, get a qualified electrician to rewire the fan if it is rotating in the wrong direction rather than attempting to do it themselves; what effect changing the positions of dampers in the system might have on other parts of the system; etc).
The potential for a dust explosion or the ignition of flammable vapour.
Appropriate techniques to visualise air flows as a means to test control:
Smoke generators and/or smoke tubes.
Dust lamp.
Physical Measurements (30%)
Common pressure and velocity measuring instruments.
Understanding of which test equipment to use for which measurements.
Where to undertake the measurements in relation to each extract point (eg, face velocity or capture velocity).
Principle of operation of a Pitot tube/manometer combination.
How to undertake a Pitot tube traverse.
How to calculate an average transport velocity from a Pitot tube traverse.
Where to undertake duct measurements to get meaningful results.
Assessment of Acceptable Performance (40%)
Understanding of the numbers produced by the tests (eg, what is an acceptable capture velocity for the application?).
Significance of transport velocity and avoidance of settling within a duct.
Diagnosis of Failures (20%)

Likely causes of the static pressure varying significantly between tests.

Duct blockages or component failure effects.
Safety Requirements (5%)
Personal protection requirements.
Permit to work schemes etc.

4.  Practical Work

Educational Objectives
Candidates should understand the principles behind the operation of ventilation systems,
be able to carry out measurements to check the effectiveness of the system, understand the limitations of this approach to controlling hazardous substances and of the crucial importance of the design element at the interface with the worker.


Candidates who pass all of the parts within 12 months will be awarded a Proficiency Certificate in Thorough Examination and Testing of Local Exhaust Ventilation Systems.

Course Duration

5 days

Number of Delegates


Candidates who pass all of the parts within 12 months will be awarded a Proficiency Certificate in Thorough Examination and Testing of Local Exhaust Ventilation Systems from the British Occupational Hygiene Society

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