The importance of good ventilation is essential for any building. An under-ventilated property can experience condensation issues and problems with air quality. An over-ventilated dwelling is usually less efficient, as lost heated air is replaced with colder unheated air from outside (with associated costs and carbon emissions from heating it). As part of a good design, buildings often follow the principle of 'build it tight, but ventilate right.' However, despite good intentions, the latter part of this mantra can sometimes be forgotten.
TWO GENERAL TYPES OF VENTILATION
GENERAL VENTILATION
Define as ventilation that controls the air environment by removing and replacing contaminated air before chemical concentrations reach unacceptable levels.
How General Ventilation Works?
General ventilation should move fresh air into the workplace and move the dirty air coming from the work out.
Reduced the concentration of chemicals in the air you breathe so it causes less harm.
Provide healthy air for breathing by both diluting the pollutants originating in the building and removing the pollutants from it.
LOCAL EXHAUST VENTILATION (LEV)
Refers to systems designed to enclose, or capture and remove contaminated air at the source.
- Use when contaminant concentration cannot be controlled by dilution ventilation or other controls.
- Select the type of LEV from hazard assessment.
- Remove airborne contaminants near their source.
- An engineering control system to reduce exposures to airborne contaminants such as dust, mist, fume, vapour or gas in the workplace. Simply put it is something that sucks an airborne contaminant out of the workplace.
A local exhaust ventilation system contains five basic elements:
- The "hood" or opening that captures the contaminant at the source.
- Ducts that transport the airborne chemicals through the system (exhaust air) and the air that is recirculated.
- An air cleaner device that removes the contaminant from the moving air in the system.
- Fan that move the air through the system and discharges the exhaust air outdoors.
- An exhaust stack through which the contaminated air is discharged.
A local exhaust system always needs a suitable inlet of clean replacement air. All industrial ventilation systems, when designed properly, should be able to provide long-term worker protection.
MEASUREMENT METHODOLOGIES AND THE LIMIT VALUES
GENERAL VENTILATION
Rule 1076.04 of the Occupational Safety and Health Standards states that “The air movement in enclosed workplaces shall be arranged such that the workers are not subjected to objectionable drafts. The air velocity shall exceed 50 ft. /min or 0.25 m/s.
Another useful guideline is given by ACGIH or Acceptable Comfort Air Motion at the Worker of the Industrial Ventilation Manual by the American Conference of Governmental Industrial Hygienist. Please take note that ACGIH is a non-regulatory organization, however, standards are recognized and adopted by most countries worldwide.
The recommended acceptable comfort air motions are as follows:
- 50-75 ft./min for air conditioned workstation
- 75-125 ft./min for general workstations, sitting (non–air conditioned)
- 100-200 ft./min for general workstations, standing (non–air conditioned)
Local exhaust ventilation system efficiency is assessed by measuring its air velocities (face, capture or duct). Air velocity ranges are based on the Industrial Ventilation Manual published by the American Conference of Governmental Industrial Hygienist (ACGIH).
LEV systems with poor air velocities cannot effectively remove the contaminants produced. In effect, these contaminants will be inhaled by the workers and may pose health risks either acute or long term. Regular maintenance of the LEV systems must be conducted to ensure their efficiencies.
HEALTH EFFECTS
Ventilation through air motion is one of the most important engineering controls for achieving thermal comfort. In industrial operations, ventilation for thermal comfort generally refers to the acceptable air motion at the workers position.
Poor ventilation is a hazard, and like all other hazards, it poses a risk to employee’s health, machines and equipment’s as well as goods and products such as:
- Leads to high levels of carbon dioxide and low levels of oxygen in the interior and can cause fatigue which affects your employee's ability to concentrate.
- Confines interior air and enhances the spread of transmittable diseases and airborne viruses, thus increasing the spread of sickness in the workplace.
- Psychological effects in the form of stress when employees are constantly exposed to ventilation hazards.
- Increased sick leave and workers absenteeism from work.
- Machine and equipment malfunctioning and damages to goods and products.
Proper ventilation of workplace removes unpleasant smells, excessive heat, smoke, fumes, excessive moisture and dust build-up by continuously replacing the interior air with cool and fresh air from the outside and, thus, prevents stagnation of the indoor air.
HEALTH AND SAFETY GUIDELINES
General Ventilation
- All workplaces need an adequate supply of fresh air
- This can be natural ventilation, from doors, windows or controlled, where air is supplied or removed by a powered fan.
- If you work in an office or shop, natural ventilation will normally be enough to control dusts and vapours from cleaning materials.
- Sometimes planned, powered general ventilation is an integral part of a set of control measures, such as welding of large fabrications in a workshop.
Local Exhaust Ventilation
- Local exhaust ventilation (LEV) is an engineering control solution to reduce exposures to dust, mist, fume, vapour or gas in a workplace.
- Use a properly designed LEV system that will draw dust, fume, gases or vapour through a hood or booth away from the worker
- An extraction system should be easy for workers to use and enclose the process as much as possible
- It should effectively capture and contain the harmful substance before it is released into the working environment.
- Air should be filtered and discharged to a safe place
- The system should be strong enough to withstand the process and work environment. It is important to maintain it and undertake tests to ensure it is working effectively.
Sources:
https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html
http://www.inchem.org/documents/hsg/hsg/hsgguide.htm
http://www.hse.gov.uk/toolbox/harmful/ventilation.htm
https://en.hesperian.org/hhg/Workers%27_Guide_to_Health_and_Safety:General_ventilation
