Category: Regulation

Even more H2

There’s a couple of Hydrogen related topics that are worth a moment. One is super conductors and the other is fire.

Heavy complex equipment like the magnets for particle accelerators use superconductors[1]. When there’s space and a need for powerful magnetics, materials with special physical properties, at extreme cold temperatures find a good use.

Talk of room-temperature superconductors is far from what it seems. Such a wonderful innovation is a million miles from any practical applications, if it exists at all. There’s no theory of high-temperature superconductivity, but there’s quite a few physicists who would like to find one[2].

Aviation researchers search for high temperature superconductors for electrical propulsion with extraordinary performance is on. The likelihood of success is low, and the timeframes are very long.

When an aircraft is flying at high altitude, the cabin altitude is maintained for the safety and comfort of passengers and crew. Air compressors, valves, sensors, and controllers make sure that cabin pressure remains at equivalent to an altitude of about 8,000 feet, and lower in some cases. So, any kind of simply flammable gasses or materials inside an aircraft cabin are a definite no no. It’s a big hazard.

In flight, the positive pressure should keep leaking gas out of the cabin. That is as long as the sources of fresh air for the cabin are keep well away from potential leaks.

That’s where Hydrogen gas can present trouble. Leaks can be common in dynamic Hydrogen systems. Storage tanks must be very strong to resist pressures and insulated to keep cold, at around –250°C. Escaping H2 gas is tiny. If that’s vented overboard then the risk of explosion or fire is significantly lowered. Knowing the exact flows of liquid or gas is a must.

However, if the gas finds its way into a pressurise cabin that basic option is limited. Not only that but detecting low concentrations of the gas in the first place is mighty difficult. Its odourless but at least Hydrogen isn’t poisonous.

The big safety issue is that the gas has a very wide flammability range (4 – 70% H2 in air mixture)[3]. Yes, H2 needs a spark to ignite. A typical aircraft cabin environment will easily provide that event. Dry air and static electricity will do it even if other sources will not.

To compound difficulties, if H2 does ignite, and not explode, then its flame may not be visible to the human eye. The flame is almost colourless. Certainly, not what most people think of as a gas flame. Gas and flame detectors could be installed in aircraft cabins and baggage compartments. Audible and visual alarms could be generated but what would be the associated crew actions?

All the above requires detailed consideration in aircraft safety assessments. The move away from prescriptive regulatory requirements means each specific aircraft configuration must be addressed. There are no generic lessons to learn from past aviation accidents and incidents.

Although, I think these puzzles can be solved it’s a huge leap from here to there.

POST: Yes, Hydrogen is not for every application. Small scale aviation is better served by electrification Five Hydrogen Myths – Busted. – RMI

[1] https://home.cern/science/engineering/superconductivity

[2] https://www.science.org/doi/epdf/10.1126/science.adk2105

[3] https://h2tools.org/bestpractices/hydrogen-flames

More H2

I think this came at me both ways as a schoolboy. Both from chemistry and physics. In our 1960s chemistry lab, Bunsen burners, flasks and array of hazardous substances were the norm. Physics seemed more cerebral. Still, the hands-on side of teaching still meant some practical experimentation. That’s the part that most engrossed me.

Electrolysis starred in two mostly harmless experiments. The colourful one was about copper sulfate[1] and the other was about splitting water into its component parts. Getting Oxygen (O2) and Hydrogen (H2) gas by electrolysis[2] is mighty simple and one of those wonders of nature.

Electrolysis is a way of producing carbon-free Hydrogen from renewable and nuclear resources. Despite the apparent straightforwardness of the process, it’s quite tricky to industrialise on a large scale. One key factor to the future use of Hydrogen is getting the cost per Kg down[3].

Let’s presume that this is a solvable problem and cheap and plentiful gas supplies will be up and running by 2030. That’s not so far off given its 2023. There will surely be a market for ample supplies given the multitude of applications for Hydrogen. Will it be a global market? It needs to be.

It’s a talking point. Hydrogen fuel is one of the viable fuels for aviation. Generating power and returning it to water in the atmosphere is an attractive idea. The process meets carbon-free ambitions even if it does have lots of complications.

On average, a Boeing 737-800 uses about 5,000 lbs (2268 kg) of conventional fuel per flight hour[4]. Cryogenic Hydrogen has lower energy density. That means much more on-board fuel storage will be needed to go as far or fly as long as a current day common commercial jet aircraft.

Designing an aircraft configuration that can accommodate these facts can be done but what of the space that remains for the payload? As it does today, on-board fuel storage will need to meet stringent safety requirements.

Adding this up, it may not be the technical issues that make this difficult. Although they are difficult the technical issues can be addressed. However, will the overall package that results be economically viable? If costs are increased by a factor of, say 5, will this provide for a commercial air transport system that is like the current one?

We may have to accept that carbon-free flying reverts to the 1960s[5]. What I mean is that, instead of low-cost flights hopping here, there, and everywhere for £100, the future maybe one where long-haul flying is a relative luxury or an expensive business need.

[1] https://www.bbc.co.uk/bitesize/guides/zgn8b82/revision/3

[2] https://www.bbc.co.uk/bitesize/guides/zv2yb82/revision/1

[3] https://www.statista.com/statistics/1220812/global-hydrogen-production-cost-forecast-by-scenario/

[4] http://www.b737.org.uk/fuel.htm

[5] https://www.skyscanner.com.au/news/airlines/the-golden-age-of-plane-travel-what-flying-was-like-in-the-1950s-and-1960s-compared-to-now

ULEZ 2

It’s not the first time I’ve experienced poor air quality. It’s a wonderful city but, on certain days of the year, the air in the German city Cologne is unpleasant. It can be stagnated, stale and dirty when the weather’s hot and there’s no wind blowing.

It was compulsory. You get a fine if you don’t have one. I remember getting a green environmental badge for my car[1]. This is a scheme by which the most polluting vehicles are banned from the central city. Introduced in 2008, initially vehicles were not banned but everyone had to have a coloured badge. These were red, yellow, or green depending upon the type of vehicle. Now, only green environmental badged vehicles are permitted to enter a prescribed city zone.

Yesterday, I drove from Reigate in Surrey to Croydon. Purley Way in fact. That’s a part of the main A23 road in the London Borough of Croydon. I now wonder at my sanity in doing so. The traffic was abominable. Purley Way is a mass of shopping warehouses, tarmac, and suburban sprawl.

What’s visible is the provisions for the introduction of the Ultra Low Emission Zone (ULEZ)[2] at the end of the month. Cameras and signs. This doesn’t ban dirty vehicles from London, but it does charge them a £12.50 daily to drive into or within the ULEZ zone. 

So, here are two different approaches to addressing poor air quality. The German one doesn’t require extensive infrastructure, but it does mean additional policing. The London one is more permissive but at a price. Collecting money from polluting vehicle owners to pay for cameras, enforcement, and publicity. Both require signage to warn drivers of the zone boundaries. Both have their detractors who object to any kind of restrictions.

To me, the problem of poor air quality can not be put on the back burner. You don’t need sensors and precision measurement to know that the problem is huge, real, and persistent. Even in my small Surrey town, the marked difference between days of traffic jams and empty roads is so evident. In the middle of COVID, I walked the High Street of Reigate, and the air was as clear and fresh as a Cornish village in winter. This week, with road works underway the town has been one big traffic jam and breathing the steamy air walking the pavement is not nice. Health suffers and it’s not just the environmental damage.

The utility of the internal combustion engine has seduced our communities. Now, the balance between the benefits of driving and the freedom it once symbolised has tipped. The sheer mass of vehicles in urban environments and their daily impact is so damaging that restrictions must be mandatory. There’s no turning back.

In Cologne, these changes are particularly pertinent. It could be said that the whole ball started rolling in that city. In the district of Deutz there’s a monument to Nicolaus August Otto[3]. He was a German engineer who successfully developed the internal combustion engine.

[1] https://www.stadt-koeln.de/leben-in-koeln/klima-umwelt-tiere/luft-umweltzone/die-koelner-umweltzone

[2] https://tfl.gov.uk/modes/driving/ultra-low-emission-zone

[3] https://www.deutz.com/en/media/press-releases/125th-anniversary-of-the-death-of-nicolaus-august-otto

Electric Flight

Hype has its place. Being positive while buffeted by the inevitable ups and downs of life is purposeful and necessary. What’s not true, and might be the impression, is that electric aviation is easy. When forging ahead to build a future, that is not yet realised, there’s a need to maintain confidence. However, being blinded by the light doesn’t help when it comes to tackling difficult problems. Proof-of-concept is just that.

The big positives of electric aviation are the environmental benefits. Electric aviation is spawning many new types of aircraft and the possibilities of new types of operation. So, there’s no doubt that this is an exciting time to be an aviation enthusiast. What a great time to be in aerospace design and manufacturing. Here we are at the start of a new era[1].

My point is that high power electrics, and their control are not “simple” or intrinsically safe in ways other types of aircraft are not. I know that’s a double negative. Better I say that high power electrics, operated in a harsh airborne environment have their own complexities, especially in control and failure management. Fostering an illusion that the time between having an idea and getting it into service can be done in the blink of an eye is dangerous.

The design, development and production of advanced aircraft power distribution, control and avionics systems is not for the faint hearted. Handling large amounts of electrical power doesn’t have the outward evidence of large spinning mechanical systems but never underestimate the real power involved. Power is power.

The eVTOL aircraft in development deploy innovative design strategies. There’s a lot that’s new. Especially all together in one flying vehicle. Everyone wants fully electric and hybrid-electric aircraft with usable range and payload capacity. So, the race is one. Companies are productising the designs for electric motors of powers of greater than 10kW/kg[2] with high efficiency and impressive reliable. These systems will demand suitable care and attention when they get out into the operating world.

A 500kW motor will go up with one hell of a bang and fire when it fails. The avionics may shut it down, but everything will have to work smoothy as designed every day, not just in-flight but on the ground too. Suppressing an electrical fire isn’t the same as a conventional fuel fire either. To fix these machines the care needed will be great. 1000 Volt connections capable of supplying high power can kill.

Not wishing to be focussed on the problems but here I go. Another major problem is the number of qualified engineers, with knowledge and experience who can work in this area. The companies who know how to do this demanding work are desperately searching for new people to join their ranks.

Educators are starting to consider these demands as they plan for the future. Sadly, there’s not so many of them across the globe who are so foward looking.

The global aviation industry needs to step-up and train people like crazy. The demand for Subject Matter Experts (SMEs) is self-evident. That’s true in design, production, and maintenance. Post COVID budgets maybe stretched but without the big-time investments in people as well as machinery success will be nothing but an illusion.

POST1 : Or 150 kW motors when you have many of them going at once. Rolls-Royce Electrical Testing eVTOL Lift Motor | Aviation Week Network

POST 2: Getting ready Preparing Your Airport for Electric Aircraft and Hydrogen Technologies | The National Academies Press

[1] https://smg-consulting.com/advanced-air-mobility

[2] https://www.electricmotorengineering.com/h3x-new-investments-for-the-sustainable-aviation/

H2 is difficult

I mentioned Hydrogen as an option for aviation. The use of Hydrogen to either power jet engines or to power fuel cells to provide electricity is a real technical option. Although the person I was talking to was engaged in environmental work, they shrugged their shoulders when I mentioned Hydrogen. They were certainly not impressed by these possibilities despite our agreement on the urgent need for de-carbonisation.

I can understand why there’s a level of cynicisms. On my part, it’s like the X-Files[1]. Fox Mulder was the believer and Dana Scully the sceptic. Broadly, I want to believe.

Today’s, liquid fuels can be explosive in certain conditions. However, it takes a considerable effort to create the conditions whereby a devastating explosion can occur. The Boeing 747-100 that was Trans World Airlines Flight 800 (TWA 800)[2] exploded, broke up in the air and fell into the Atlantic Ocean in 1996. This was an example of a worst-case scenario. 230 people were lost in that fatal accident. Now, the ignition of a flammable fuel/air mixture in aircraft tanks is better prevented by design and operational procedures.

If Hydrogen is to be viable in civil aviation such hazardous conditions will be harder to prevent. A flammable hydrogen/air mixture can be ignited much more easily than conventional liquid fuels. Such dangerous situations can be prevented but the measure to do so will require robust design and stringent operational procedures.

Several development programmes are underway, making practical Hydrogen powered aircraft viable. A range of aircraft configurations are possible. From hybrid generator and electric motor set-ups to combustion-based propulsion. This work is moving from academic research into commercial possibilities.

There little read across between the behaviour of conventional hydrocarbon liquid fuels and liquid Hydrogen. This would be evident in any serious incident or accident scenario. Let us imagine the case of British Airways Flight 38, in 2006, a Boeing 777-236 that came down at the end of a runway at London Heathrow[3]. A significant amount of fuel leaked from the aircraft after it came to rest, but there was no fire. There were no fatalities.

The breakup of liquid Hydrogen tanks or plumbing in such a scenario would almost certainly result in a significant fire. The mitigating impact of that fire is the lightness of the gas. Instead of liquid fuel pooling on the ground, Hydrogen would burn upward. However, any explosion could be devastating.

So, for large aircraft design the provisions to protect liquid Hydrogen tanks and plumbing must be extensive and extremely robust. This would have to be maintained, as such throughout the whole operational life of the aircraft. These requirements would be onerous.

Keeping crew and passengers well away from Hydrogen infrastructure will be a must.

POST 1: Crashworthiness doesn’t get much of a look-in. Without it there’s going to be a problem over the horizon. https://www.ati.org.uk/flyzero-reports/

POST 2: At least for eVTOL aircraft some work is being done. https://ieeexplore.ieee.org/document/10011735

[1] https://www.imdb.com/title/tt0106179/

[2] https://www.history.com/news/twa-flight-800-crash-investigation

[3] https://assets.publishing.service.gov.uk/media/5422ec32e5274a13170000ed/S1-2008_G-YMMM.pdf

No shock

It’s very easy to have the false belief that – I’d never do that. Such phases top the bill. Of course, the one that really tops the bill is – well, I haven’t had an accident yet.

Most accidents and incidents happen in the home. When I say that, I include the garden and places that are extremely familiar. I suppose it’s the habit of taking the status-quo for granted that lulls us into a false sense of security. I’ve known several tragedies where seemingly benign situations have turned out disastrous.

Cutting through a hedge trimmer cable can be dangerous. I didn’t do that. Besides, the makers of hedge trimmers have made it difficult to get electrical shocks from their products. The extensive use of plastics, double insulation, two-wire connections and Residual Current Device, or RCD have made us a lot safer, however foolish we might try to be. An RDC is one of the most important electrical safety devices in everyday [1]use. A mains electrical current of a few milliamps (mA), for a second can be enough to kill a healthy person. My own experience of electrical shocks puts me in the lucky bracket.

So, what did I do? It’s like this. I have a large wooden shed in the garden. It’s supplied with power by a bright orange electrical cable that is hung high in the air from my garage to the shed. I even created a wire catenary to ensure that there is no stress on the electrical cable. It’s not new. It’s been there for a couple of years.

My bright red budget hedge trimmer is battery powered. It’s light weight and easy to use. That’s good – isn’t it? No problems with cables that may become damaged or frayed. It needs two handles to be squeezed to make it work.

Trouble is the ease of use means that the trimmer can be picked-up quickly to do a 5-minute job. That’s what I did. I thought, I’ll quickly trim back the overgrown honeysuckle that’s covering a fence. Slap the battery in and bish, bash, the job is done. Very straightforward job.

From here the story tells itself. Yes, such haste is never wise. The sweeping movements of the trimmer did the job they were supposed to do. They did something more too. There’s lots of stories about cutting through an electrical cable with a hedge trimmer. Sadly, that’s what I did.

The emotions after the event must be common place. How could I do something so stupid? For heaven’s sake the cable is bight orange. It’s high up. Why was I so careless?

Then there’s the feeling that comes later, however stupid the act might be there’s no injury to anyone. The RDC tripped, as it should. Immediately, I turn the power off in the garage. Now, I have two dangling parts of what was once a complete overhead cable. My damaged cable is going to need a waterproof repair. That’s the next job.

If there’s a lesson, it may be that none of us are immune from error. Common problems are common problems for a reason. The human factor is real.

Local air

There are cases of synergy. That’s where aviation and local authorities have a mutual interest. This often centres around the economic prosperity of an area. Relationships can be complex, difficult, and fraught with volatility. There are plenty of housing and industrial estates that cover the ground of former airfields. Like the railways that closed under Beeching’s axe[1].

Public interest was dominant 50-years ago, but privatisation dramatically changed relationships. Sustaining profitability through good times and bad have proven to be more than some locations could support. There’s so many combinations and permutations but fewer and fewer active commercial airfields in the UK.

London Manston Airport is an airport that only just clings on to existence. In 2013, the Welsh Government acquired Cardiff Airport. So, some aviation facilities have returned to public ownership and run as an arm’s length business. A few airports are given support to ensure connections exists between remote parts of the UK. Highlands and Islands Airports is an example.

Advanced Air Mobility (AAM) is coming. This is the extensive use of electric vertical take-off and landing aircraft (eVTOLs). AAM is an innovative concept that will require Vertiports and integration into busy airspace. To make the economics work a lot of routes will be in, and over urban areas.

My view is that AAM will only succeed in the UK if aviation and local authorities come together and embrace it. That is going to be a massive challenge whatever national government does.

In the case of local authorities with a mission of protecting the interests of residents this has often meant objecting to aviation developments. I go back to proposals of 30-years ago to make Redhill Aerodrome a feeder to London Gatwick Airport[2]. This was well and truly shot down by local interests. In fact, rightly so given the complex twists and turns it would have made in the airspace.

AAM needs the harmonisation of standards to ensure interoperability anywhere in the country. There are one or two UK local authorities that are already embracing the potential opportunities of this new form of flying. Coventry City Council is taking on the challenge[3]. It’s welcoming the development of the ground infrastructure for “air taxis” and delivery drones.

By the way, my view is that introducing the subject as “flying cars” or “air taxis” is not a good idea. This creates images from science fiction that may not resemble the reality of these new air services.

[1] https://www.networkrail.co.uk/who-we-are/our-history/making-the-connection/dr-beechings-axe/

[2]https://john-w-vincent.com/wp-content/uploads/2023/08/bf3ec-clear_for_take_off.pdf

[3] https://www.coventry.gov.uk/news/article/4232/world-first-hub-for-flying-taxis-air-one-opens-in-coventry-uk-heralding-a-new-age-of-zero-emission-transport

Over the Horizon

Reading Anne Corbett’s article on the Horizon Europe research programme[1], I’m struck by the one step forward and then one step backward walk that the UK is taking. The politics of the moment leaves a UK Prime Minister (PM) dancing on a knife edge. Afraid to fall to the right or to the left of his own party. Having been part of an extremely destructive period in British politics, Rishi Sunak is attempting to re-brand the Conservatives with a colour of nationalism that’s designed to be anything to everybody and as variable as the wind.

From the start of the year, Rishi Sunak has made five promises[2] on economy, health, and immigration. The one on the economy is steeped in blandness. This is presumably to claim success regardless of the situation in the run-up to the next UK General Election. If a PM, of any political party, didn’t want to grow the economy, create better paid jobs and opportunity across the country there would be something distinctly wrong. A wish is fine but what about actions?

I have to say that it’s good to see a UK PM that’s 20-years younger than I am. Particularly when the US is playing out a game of geriatric musical chairs. Russia being plagued with the politics of generations past. China’s building global influence. And to top it all the Earth feeling the impact of climate change like never before.

This why I have such difficulty in understanding Sunak’s attitude to working with our nearest neighbours and closest allies. We have more common interests now than we did in the 1970s when the UK first joined our local trading block. I’m sure the zealots can’t see this fact but undoing the last 40-years is not a good way to forge a future. We can do so much better.

Culham is known for its Centre for Fusion Energy[3]. Its work is collaborative. It needs to be, given the huge costs of working in the field of fusion energy. That’s the way the Sun generates its energy. Here’s an example of the UK being a focal point for European fusion research. Post Brexit, like the problems other research institutions have faced, some researchers returned to continental Europe.

The idiocy of de-Europeanisation serves no one. It’s a residual of discredited political thinking. A Government doesn’t need to advocate re-joining the European Union (EU) but they do need a whole new positive approach to working together with European countries and institutions. Research is at the core of our common interests.

[1] https://blogs.lse.ac.uk/europpblog/2023/07/28/will-the-uk-find-its-way-back-to-horizon/

[2] https://www.bbc.co.uk/news/uk-politics-64166469

[3] https://ccfe.ukaea.uk/

Short-sighted

None of that comes cheap.

OK. Why are mini-nuclear power stations such an irrational idea? The industry is selling these untried, untested power station as completely unlike that which has gone before. A Conservative Minister has been echoing their marketing brochures.

Let me say, with power generation there are some basic realities that remain the same.

Fuel must be transported to power stations and waste must be removed from them on a regular basis. For coal, that was the reason for the sitting of large power stations in the past. For gas, there was more flexibility in location, but the costs of transportation still needed to be minimised. For such innovations as waste-to-energy plants, proximity to the source of waste presented a major problem. Neighbourhoods rarely invited these plants to be built close by.

Spreading the distribution of nuclear fuel and waste around the country doesn’t sound like a good idea to me. Cost of transportation are high. Safety is paramount. Security is always a grave concern.

Now, I understand the need for limited numbers large-scale nuclear power stations. They provide a reliable base load when the renewable sources of power are not available. The wind doesn’t blow.

Although, there are a variety of different international companies in the nuclear business the notion of a “free market” in the conventional sense is not a real prospect. The investments needed to be competent and meet regulatory requirements in the nuclear business are huge. Projects are there for the long-term. A whole working career of a nuclear engineer may be locked to one technology.

Experience has shown us that a goal of zero accidents rarely delivers a reality of zero accidents. These are complex engineered systems. It doesn’t matter if they are big or small the complexities remain. Yes, safety can be managed in a safety critical industry but there had better be preparedness for worst possible outcomes[1]. With these nuclear plants decommissioning and recovery from significant incidents of contamination must be accounted for in any design, implementation, and operation. None of that comes cheap.

Overall, in Britain there are much better paths to travel than the mini-nuclear one.

It absolutely astonishes me that, given the enormous tidal range of the Severn Estuary[2] we have never captured the energy of those waters. Equality in a nation, with a coast as large as ours, we have only ever dabbled in wave power[3]. Let’s have some genuine innovation. Let’s think like the Victorians and build for the long-term.

Why are we so incredibly short-sighted in Britain?

[1] https://www.bbc.co.uk/news/world-13047267

[2] https://en.wikipedia.org/wiki/Severn_Barrage

[3] https://en.wikipedia.org/wiki/Salter%27s_duck

Bad Smell

Where is the accountability?

My desk, that’s the one in the early 1990s, faced towards the London Gatwick airport approach. It was a good reminder of the business we were in at the time. Seeing aircraft land and take-off about 500 m from the sheet glass windows of our office block was the daily background. Being in a rugged hermetically sealed building aircraft noise wasn’t a great concern.

Little more than 300m from the building and looking in the same direction was, and still is, the Gatwick sewage works. Its structures were low rise, so it was often hidden behind the greenery. Every so often, a strong wind would blow from the northeast. When it did a distinct odor filled the air. Yes, you guessed it. The sweet smell of the sewerage works would permeate the air conditioning.

This odor was at its most notable in the metrological conditions called an inversion[1]. In fact, given the seasonal frequency of these weather conditions it could be said that Gatwick wasn’t the most sensible place to build a major airport. These occasional pongs were a bit of a joke. Along with the occasional smells of unburnt aviation fuel it was just life at the airport. Lingering odors didn’t stay for long. A day at most and the wind would change direction back to where it normally came from – the south west.

Airports and sewage works are not a good combination for the health of rivers and streams. Long ago, when Gatwick airport was built the tributaries of the River Mole[2] were diverted. The part of that river, the Gatwick stream going north to south, at the end of the runway, is an unattractive V-shaped gully. Not nice for nature at all. There was a track that ran parallel with the river. In the summer, I’d walk that track at a lunchtime as it was a way of getting to the airport’s south terminal.

In the news, Thames Water are being fined for dumping raw sewage in the River Mole[3]. The consequences of the UK’s water regulator[4] taking a relatively hands-off approach to managing water companies, since privatisation in the late 1980s, has come home to roost.

I must admit, I’m not the least bit surprised. So far, the dance of those who shrug their shoulders astonishing. Ministers, regulators, company chiefs are all pointing fingers at each other.

The sequence of events is mind blowing when looked at over several decades[5]. Chief executives attracting massive salaries. Companies being loaded up with debt. Generous payouts to shareholders. Investments in infrastructure not keeping pace.

Ofwat, the regulator talks with incredible complacency. Such weak regulators are no more than a piggy in the middle as the powerful forces of unethical commercial behaviour and disinterested government oversight combine. As millions of families struggle with the cost of living this kind of failure is intolerable. Where is the accountability?

[1] https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/temperature/temperature-inversion

[2] https://www.southeastriverstrust.org/river-mole/

[3] https://www.independent.co.uk/news/uk/crime/thames-water-sewage-spill-gatwick-airport-b2368707.html

[4] https://www.ofwat.gov.uk/

[5] https://www.bbc.com/news/business-66103356.amp