Actually the serious point is: you need to be pretty nifty to work in a prison, bceause of....security, and typically long runs of tortuous, small cross-section, ductwork

It can often be useful to survey kitchen exhaust or extract systems form inside to check where they run, and what their condition is. Many specialists a video extension tool like the Triventek Minicam. Basically it gives you the ability to look up to 8/15metres distant in a duct system and can be pushed round bends etc

He also gets on to talking about particle count testing of filters, and reminds me of this important point when thinking about filter efficiency:

To give you a feel for what your typical filter is up against, here is a plot of atmospheric particle count by weight and size that I developed from a couple of industry resources.

Basically, the graph says that there are zillions of little tiny particles in the air all around us, but they are so small that they don’t contribute much to the total weight of the particles suspended in the air. So, that means, in a general sense, that eliminating the big stuff; i.e. the stuff that tends to be pretty easy to filter out, really won’t eliminate much of the fine stuff that is really our target. A low efficiency filter does great job of catching the occasional “boulder” that is in the air stream, but by and large, doesn’t do much to stop the “pebbles” that comprise the bulk of the contaminants its exposed to.

In the old days the filter classification systems were effectively set up so that every filter could be described as >95% efficient. The question was always 'against what challenge?' - house bricks or combustion products?

It seems it hasn't been a great building for 36 years.

Regarding air hygiene, various tests and investigations have been done, but none have produced results convincing enough for the employer/landlord to do anything concrete about duct cleanliness

A couple of quotes from the article:

"Employees also spoke of black, dustlike particles falling from ceiling vents. County officials said that was a concoction of dust and dead skin and was not a health hazard"

“People start wondering what the test results mean,” he [State Health Dept investigator] said. “Interpretation of the results is difficult. (People) want to link mold in the environment to their health issues, and that’s a problem because we don’t have a benchmark for what is safe and unsafe.”

Now take a look at the state of an HVAC diffuser grille and the nearby ceiling as an office employee takes a tape sample for mould / mold

And yes I know some of that dirt is induced from the served area onto the grille vanes and ceiling tiles, but really - how filthy does a building component have to be before somebody says: 'Hey, let's clean this'?

Think of the time and money that's been spent over the years doing investigations, discussing results etc. Is it really that complicated or difficult to see that it's just not right for a system to be that dirty?

It's the old story: just because it's out of sight, does not mean it should be out of mind.

Here's an example of what I call "selling with a truncheon in your hand"

But the points are well made. Local Exhaust Ventilation (LEV, provided typically in the industrial workplace to remove hazardous airborne contaminants ranging from sawdust, through to gases and fumes) extract ductwork can get dangerously dirty. They fall, in the UK, under the Control Of Substances Hazardous to Health (COSHH) Regulations, and regular functional testing should be carried out to prove that they continue to provide the 'control measure', i.e. reliably pull out the contaminant. Similar Regulations whereby effective control measures should be in place for control of workplace contaminants exist in most countries.

Often the engineer responsible for the systems wants to clean the LEV system, because he knows that's the right thing to do, but he needs 'The Law' to convince his superiors that something should be done.

Of course LEV sytems should be designed so that the contaminant stays airborne and does not settle out on the duct surfaces..but it doesn't always work out like that. Not by a long chalk!

You can see deposits build up which will impede airflow (and so stop the system properly pulling workplace contaminants away from the worker's breathing zone). Often enough air velocity can be slowed down by a gradual accumulation of dusts, or by a larger item like a paper wrapper, piece of packaging, beer can (no really! where's a better place to hide the evidence of illicit drinking?), which then allows finer dirt to build up.

Besides airflow reduction, there can be an issue with the flammability of the material caught in the duct. The material can act as a fuse and carry fire through the building

Here's an example of an industrial laundry extract duct whose cross-sectional area has been reduced. Not only was there an efficiency problem (the hot, moist air was not being properly removed, also there was significant fire risk - laundry extracts go up quite often).

Just a quick commercial break for Triventek duct cleaning equipment: the rotating brush nozzle is perfect for cleaning some of the more adherent deposits you can find in LEV extracts. You have the combination of Jetvent Tornado nozzle 'sticking' to the duct surface. PLUS the cleaning aggression of a wire brush spinning at 9-11,000 rpm.

The Rotating brush nozzle only works on circular ductwork, but that's no problem since the great majority of LEV ductwork is circular.

One warning note: do make sure that you know what the contaminant is and how to deal with it, from a toxicity point-of-view, and possibly from a flammability point-of-view

This story is great, made all the better by the (to English ears) weird sound of the name 'Cillit Bang'.

Seriously though, Triventek duct cleaning equipment is actually used at Dounreay for cleaning the internal surfaces of ventilation ductwork, before it is pulled out and de-commissioned.

There's some discussion of cleaning radioactive dusts out of ductwork in the main site's FAQ section

This one about Mark Scobbie in Falkirk, Scotland is hilarious.

Wouldn't it be great if the barman had managed to take a photograph?

So another point to add to the duct cleaner's training course: 'Why taking your trousers off is a bad idea'

It does re-iterate some of the simple virtues of keeping buildings clean and dry, and critically for HVAC systems:

"Several studies have shown that the prevalence of symptoms of sick-building syndrome is often higher in air-conditioned buildings than in buildings with natural ventilation (Mendell, Smith, 1990; Seppanen, Fisk, 2002). One explanation for the association between sick-building syndrome and mechanical heating, ventilating and air-conditioning systems is microbial and chemical pollutants, which are emitted by heating, ventilating and air-conditioning components and ductwork".

You can download a copy of the Guidelines from our website here

There is of course also much emphasis on keeping buildings (and HVAC systems) dry, and on dealing properly with condensation where it is unavoidable e.g. at a cooling coil.

As practical experience shows, the majority of 20th century A/C systems (and a pretty large proportion of those installed in the last few years too) do not have properly designed and installed condensate drain trays and so you get trapped water. This is one of the reasons we've been so keen on Triventek BioBlock to stop microbiological growth where stagnant water cannot be avoided.

In the dirty ducts, evidence of methicillin-resistant Staphylococcus aureus (MRSA) was found in 9 out of 14 samples. After cleaning, using the Jetvent high-volume compressed air cleaning system, all 14 samples were negative for MRSA.

This is a significant finding as hospital infection control officers press to reduce reservoirs of infection throughout hospital and healthcare facilities

You can download a pdf of the article, called HVAC Central in Hospital Hygiene

 For those of you who haven't seen this on the main website, here's a youtube upload of the video demonstrating the Jetvent Hi-Aire duct cleaning equipment.

It's good to have video for this because you can really see how high volume compressed air 'sticks' to the duct surface. That's the basis of its power and is the big difference with e.g. North American 'skipper' balls which work randomly. All this, and it's fantastically low cost too! For what it does, it's a steal.

This picture is interesting, illustrating as it does some of the variety of materials that can be found in ordinary household dust:

Although house dust is known to be a predominant source of exposure to PBDEs, it's not yet clear which part of the dust these chemicals bind to. The dust pictured above contains pet hair (rust brown), pollen (yellow), plant fibers (green), dead skin cells (light to medium brown), dirt and minerals (orange), textile fibers (blue), and spider silk (pink).

This picture came from an article about PBDE's (flame retardant chemicals) found in common dust, and in the bloodstreams of occupants

It seems that the duct was suspended on wire, rather than traditional hangers, presumably for cosmetic reasons as it was exposed.

It's still puzzling as to how these could have failed: guess we'll just have to wait for the report, and hope it gets some publicity to alert us

I presume that this would have been relatively large cross-section ductwork as is typically found in sports halls etc

The hospital management have made a ridiculous claim: "Evans said no one anticipated the new unit would blow air so forcefully it ballooned the air ducts, allowing the dust to get around three filters and into the operating rooms."

That's a literally incredible idea.

Normally you'd say Evans has been mis-reported by a non-technical journalist, but I don't imagine that the word 'ballooning' could get easily get mis-reported.

I suppose this sort of nonsense is inevitable whan a blame game gets into the public prints

It's articles like this that make me wish for American-style levels of HVAC in the home.

But also: isn't it great how Americans always want to share what they know - just made for the internet, or is it the other way round?

 Here's an interesting story about an American sugar plant, whose dust extraction systems were inefficient, which led to 'plugging up' of ductwork, which led to excess airborne dust, which led to explosion and fire killing 14 workers

In this story about a cheating contractor not properly cleaning a duct,  and putting at risk the 12 occupied floors above, he reminds us about just what a responsibility the contractor carries.

And also about the responsibility of the employer who alterted to the problem, simply replied: "They are half your price so we will stay with them"

Singaporean academics specialising in environmental health and safety, and in public health epidemiology have recently been reported to be concerned both about dirt and debris in ducted air conditioning systems, and about condensate, especially in the humis local environment.

"If, for instance, dust and mould form as a result [of poorly maintained HVAC systems], symptoms of allergic rhinitis, an inflammation of the nasal passages, and asthma can worsen", said Dr Hwang Siew Wai, director of the Bukit Merah SingHealth Polyclinic.