Avoiding Confined Space Hazards: A Simple Guide to Measuring Air Flow

8th September 2021

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It’s hard to overstate just how important the correct level of air flow is for projects where the inherent hazards created by confined space working are present.

That’s why we’ve created this quick read overview and included our free, essential airflow performance reference charts (see below).

While the risk created by lack of air flow in a confined space might be obvious, it’s worth reminding ourselves that the HSE’s own confined space working guide pulls no punches when it warns that “a number of people are killed and seriously injured in confined spaces each year in the UK”.

Our quick read overview looks at the role air flow measurement plays in addressing this risk.

Confined Space Hazards & Air Flow: A Quick 101

Our Safe Working in Confined Spaces primer covers many of the essentials around confined space hazards.

As a quick recap: the HSE describes a confined space as “any space of an enclosed nature where there is a risk of death or serious injury from hazardous substances or dangerous conditions (eg lack of oxygen)”.

This could mean some obvious spaces with a limited opening like storage tanks and enclosed drains but could also refer to less obvious work sites such as open-topped chambers, ductwork or even unventilated or poorly ventilated rooms.

The HSE documentation also lists some possible, serious risks:

• “A lack of oxygen. This can occur: where there is a reaction between some soils and the oxygen in the atmosphere; following the action of groundwater on chalk and limestone which can produce carbon dioxide and displace normal air; in ships’ holds, freight containers, lorries etc as a result of the cargo reacting with oxygen inside the space; inside steel tanks and vessels when rust forms.”

• “Poisonous gas, fume or vapour. These can: build-up in sewers and manholes and in pits connected to the system; enter tanks or vessels from connecting pipes; leak into trenches and pits in contaminated land, such as old refuse tips and old gas works.”

• “Liquids and solids which can suddenly fill the space, or release gases into it, when disturbed. Free-flowing solids such as grain can also partially solidify or ‘bridge’ in silos, causing blockages which can collapse unexpectedly.”

• “Fire and explosions (eg from flammable vapours, excess oxygen etc).”

• “Residues left in tanks, vessels etc, or remaining on internal surfaces, which can give off gas, fume or vapour.”

• “Dust present in high concentrations, eg in flour silos.”

• “Hot conditions leading to a dangerous increase in body temperature.”

It is also pointed out that among those killed due to this type of hazard have been those who have tried to rescue operatives “without proper training and equipment”.

An online HSE resource details legislation essentials refers to a case study in which deaths occurred following work on a crane’s hydraulics: the tragic deaths involved both a man who had entered the crane to work and a man who had attempted a rescue.

The HSE states that, in their case study involving these confined space working deaths: “Water had got into the compartment causing rusting, which depleted the oxygen levels. Had the oxygen levels been checked, the space could have been ventilated and the deaths could have been avoided.”

Confined Space Hazards & Air Flow: Measuring Air Flow

Airflow is, therefore, an essential factor in reducing the risks surrounding confined space working.

However, the performance of fans – bearing in mind that not all will perform identically – can vary depending on some vital factors:

Ducting: When ducting is attached to the inlet, outlet, or both the inlet and outlet, of a fan its performance is changed. The possible configurations are…

  • Free inlet, free outlet
  • Free inlet, ducted outlet
  • Ducted inlet, free outlet
  • Ducted inlet, ducted outlet
  • Ducting length
  • Fan size
  • Bending the duct: For example, around a corner
  • Straight lengths of flexible ducting connected to an Air Mover will vary per application
Our at-a-glance guide to air flow performance is available here and covers essential configurations of free and ducted air flow including Air Mover performance charts.


Equipment for the Life-And-Death Environments

You can find out more about our renowned portable EX ventilation equipment here. But we’re much more than just an equipment ‘supplier’. We actively help our clients safely achieve optimal ventilation, heat, power and lighting results in challenging environments using stand-alone – even bespoke - solutions.

What makes SA Equip different? We bring almost 100 years of pacesetting service and knowledge - with a foundation in the most extreme shipping and oil industry environments – to global clients across aerospace, shipping, defence, utilities, pharmaceuticals, distilling, power stations and more.

This means SA Equip portable air, light, heat and power products have been proven in challenging conditions offshore, in the air and beyond for almost a century.

Contact us

for help with choosing the right equipment including off-site LEV solutions, to request a demonstration or to find out more about our bespoke equipment service.

See also: Safe Tank Cleaning Procedures, Safer Working Without Hot Work Permits