The first question you might ask is why ventilate? There are many good reasons to ventilate, but environmental stability tops the list. David Angelico, president of Air Systems, has this to say: ‘Ventilation of a confined space should be done to stabilise the environment. This provides us a reference point for the most important piece of confined space equipment – the atmospheric monitor. This “stabilisation” of the confined space atmosphere minimises the speed at which the atmosphere can or will change and maximises the reaction time by the worker to evaluate the change and decide if they need to exit the confined space.’
This basic understanding significantly reduces worker risk, identifies the hazards of confined space entry and puts to rest the question, ‘Should I ventilate?’ Understanding this concept also addresses the need for respiratory protection. Ventilation of a confined space area does not preclude the use of respiratory protection. While ventilation may make the atmosphere stable for work, it does not necessarily make it breathable. The work being performed could easily cause the atmosphere to change and would dictate the use of respiratory protection.
So here’s how to do it – and do it properly.
When is natural ventilation unfavourable?
- Lack of air movement in and out of the space can create an atmosphere much different than the outside atmosphere.
- Deadly gases can be trapped inside.
- Organic materials can decompose.
- May not be enough oxygen due to presence of other gases or chemical reactions, such as rusting.
Overcoming natural ventilation problems
- You must establish techniques and procedures to provide adequate ventilation.
- It is easier to work with than against natural convection.
Two reasons to use mechanical ventilation
It can properly reduce or eliminate respiratory protection requirements.
Effective engineering controls are usually less dependent on worker attention than respiratory protection.
Basic ventilation requirements
Although a single rule or group of rules is unlikely to cover all of the ventilation requirements applicable to confined spaces, the objectives of ventilation in confined spaces are the following:
- To remove contaminated air (flammable or toxic) from the space and maintain safe concentration levels in terms of permissible exposure level (PEL) or lower explosive limit (LEL), using the most convenient one.
- To provide fresh and breathable air inside the space.
- To create a more comfortable environment inside the space.
You can only achieve these objectives after a thorough evaluation of the requirements, based on:
- the confined space under discussion
- its content, and
- the operations you will perform in the space.
You can calculate your ventilation requirements based upon space and operational aspects. You must base the evaluation of ventilation on the measurements that you take of the ventilation system or the atmosphere of the space, to guarantee that you achieve safe conditions and that you can maintain them.
Ventilation required before entering or working
Confined spaces must be ventilated before entering or working to the degree necessary to reduce flammable and toxic substances to acceptable levels and to provide adequate oxygen content inside the space.
Ventilation required to enter and work
The operations that are performed inside a confined space may require the application of a single type of ventilation, such as general ventilation, or may require the application of two types, such as general ventilation combined with a local exhaust ventilation system.
What is general ventilation?
General ventilation is often used, alternating it with air dilution.
What is local exhaust ventilation?
A local exhaust system consists of an arrangement in which the exhaust intake (opening with a duct or bell) is placed near the point of work where the contaminants are generated. A local exhaust system captures the contaminants as they are generated, carries them to the duct of the system and expels them from the work site. To remove the contaminants that are generated in a single point, as in welding, or in localised clean-ups with solvents, local exhaust systems are more effective.
What is dilution ventilation?
This is done by incorporating uncontaminated air inside a space to dilute the contaminated air that is inside until an acceptable level is achieved. Dilution ventilation refers to dilution of contaminated air with uncontaminated air in a general area, room or building, with the purpose of controlling any hazard or discomfort to health. However, usually dilution ventilation is not a control for a hazard to health as satisfactory as local exhaust ventilation. However, occasionally, this ventilation mechanism must be used in circumstances where the operation or the process performed prohibits the use of local exhaust ventilation.
What is dilution and exhaust ventilation?
This type of ventilation consists of incorporating uncontaminated air inside a space to dilute contaminants, combining them with an exhaust localised at the area of greatest generation of contaminants, utilising flexible ducts.