Monthly Archives: October 2010

Why change the clocks?

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Because the Earth is tilted on its axis, the length of the day (i.e. the time between sunrise and sunset) changes throughout the year. During summer in the northern hemisphere the North Pole is tilted towards the Sun and days are longer and warmer, and during winter the North Pole is tilted away from the Sun and the days are shorter and colder.

The change in the length of the day depends on latitude; the further north or south you go, the greater the variation.

For London, in 2011, the length of the day will change as shown below:

When British Summer Time is taken into account the pattern changes:

BST enables us to make better use of the available daylight by shifting hours of sunlight from the morning to the evening; it takes hours of daylight from the morning whilst most people are asleep and “moves” them to the evening when most people are awake. The term used in the US – “daylight saving time” – makes this more obvious.

Having more hours of daylight in the late evening reduces the use of electrical lighting. The environmental campaigners 10:10 (the same group that made that awful video) and others have been pushing for the permanent adoption of BST, with an extra increase of an hour during the summer, a system called Single/Double Summer Time (SDST).

The Royal Society for the Prevention of Accidents has suggested that moving to SDST would reduce accidents, benefit tourism and leisure and help prevent crime. Conservative MP Rebecca Harris has submitted a Private Member’s Bill that is currently before Parliament asking the Secretary of State to consider making this change.

The “compensation culture” does not exist

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Blaming “Health and Safety”, and by extension the Health and Safety Executive (HSE), seems to be the new “political correctness gone mad”. Newspapers are full of stories about how the UK’s “compensation culture” impacts negatively on daily life in the UK.

The thing is, it doesn’t exist. There is no “compensation culture” in the UK outside of the media, and the stories you hear about the HSE banning things right and left are that and only that: stories.

Lord Young of Graffham’s report Common Sense, Common Safety (685kB, .PDF), “a Whitehall-wide review of the operation of health and safety laws and the growth of the compensation culture” was published on 15th October and makes it very clear that that the media has a lot to answer for in perverting the work of the HSE:

“[T]he standing of health and safety in the eyes of the public has never been lower. Almost every day the papers compete to write about absurdity after absurdity, all in the name of ‘elf and safety’ as it has become widely known.

“The problem of the compensation culture prevalent in society today is, however, one of perception rather than reality.

“There was an overriding opinion that the health and safety agenda had been hijacked by the tabloid press, whose reports often contributed to misinterpretation and misunderstandings by regularly exaggerating and ridiculing instances which in reality have little or nothing at all to do with health and safety.”

(Emphasis mine.)

One of the most telling sections of Lord Young’s report (Annex D, if you’re reading along) compares media stories with reality. The tragic case of Jordon Lydon, a 10-year old who drowned whilst fishing for tadpoles, is perhaps the most striking. The story was reported at the time (e.g. by the Daily Mail and the Daily Express) in sensationalist terms:

“[A]ccusations were made that the policemen involved stood by and watched a boy drown because health and safety rules forbade them from entering the water to save him.”

But the reality was far simpler, though no less tragic:

“The boy’s step-father and friend arrived at the pond just before the police officers.They immediately dived into the water and brought the child to the surface.The police officers then arrived and one of them dived into the water and helped to bring the boy onto the bank. Unfortunately by this point he had been underwater for 20 minutes.”

I can only hope that the media report on Lord Young’s report with all the fervour that they reserve for stories about “‘elf and safety”. I’m not holding my breath.

On another issue close to my heart, Lord Young specifically addresses the issue of educational trips.

“There have been a number of cases where schools have prevented pupils from taking part in educational visits citing health and safety as the reason for non-participation. The process for taking children on educational visits involves a huge amount of form-filling – ranging from consent forms to risk assessments …

“This process can involve excessive bureaucracy that is not proportionate to the role it plays in reducing the risk of accidents. It merely serves as a deterrent and an excuse to ‘do nothing’.

“As a consequence, children are potentially missing out on vital education because schools just do not have the time and resource to carry out the process and, if they do, they are too concerned about the threat of legal action should an accident happen.

“We should introduce a single consent form, signed by a parent or guardian, which covers all activities a child may undertake during their time at a school, enabling parents to opt out of any specific activities. Consent is already not required for activities which take place during the school day and in order to reduce the amount of bureaucracy around school trips we should underline this message to schools and local authorities.”

(Again, emphasis mine.)

See also:

Colour temperature and f.lux

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All objects emit electromagnetic radiation, and the type and amount of radiation emitted depends on the object’s temperature. The hotter the object, the higher the energy of the emitted EM radiation: a cold object will emit radio waves and as temperature increases, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays.

The surface of the Sun is about 6000K which means that it produces light right across the spectrum, peaking in the green. It is this green coloured light that humans (and other land mammals with colour vision) are most sensitive to – you have twice as many green-sensitive cones as red- and blue-sensitive ones.

A standard incandescent filament lightbulb uses a titanium filament at a temperature of 1500K. This is significantly colder than the Sun which means less higher-energy green and blue light is emitted, leading to an overall yellow colour. Flourescent lighbulbs do not work in the same way so their colour temperature is adjusted by altering the mix of phosphors inside the bulb.

Left to right: simulated 6500K, 2000K, 2650K and 3000K compact fluorescent bulbs

I spend a lot of time in front of a computer screen; something that is not good for the eyes. I have a program called f.lux installed on my laptop that adjusts the colour temperature of my monitor automatically throughout the day; during the daytime the colour temperature is 6500K, after sunset it drops slowly to 3400K. This helps to reduce eyestrain and maintain circadian rhythms.

Long half-life ≠ dangerous

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Nuclear waste is often quoted as having a “half-life of millions of years” as if this is a bad thing in and of itself.* But there’s another way of looking at it.

Radioactive decay occurs when an unstable atom emits either a helium nucleus, a high-speed electron, an electromagnetic wave called a gamma ray or more rarely one of a number of other possibilities. Being in the way of these emitted particles and waves is generally considered to be a Very Bad Idea.

Radioactive decay occurs at random, with each atom having a chance of decaying at any given moment. The more likely it is that atoms decay, the quicker they decay, and the shorter their half-life.

Imagine the radioactive atoms are ammunition cartridges; when they decay the cartridge “goes off” and a bullet is released. Now imagine you’re standing next to two piles of cartridges representing some nuclear waste: one pile with a short half-life and one pile with a long half-life

The bullets in the short half-life pile will go off over a short period of time, and the bullets in the long half-life pile will go off over a longer period of time. Which pile would be safer to stand next to?

Caesium-135 and caesium-137 are both common isotopes found in nuclear waste: Cs-135 is formed when xenon-135 produced as a fission fragment decays by beta emission; and Cs-137 is formed as a fission fragment itself (a uranium nucleus splits to form one caesium-137 and one rubidium-98 nucleus).

Cs-135 has a half-life of 2.3 million years and emits beta particles with an energy of 267 keV. Cs-137 has a half-life of 30 years and emits beta particles with an energy of 605000 keV. On a graph of 100 years the change in caesium-135 is invisible; only at a scale of a million years does the change become visible:

If you stood next to a million atoms of Cs-137 for a year 22840 atoms would decay, for a total energy release of 2.2 nanojoules. Standing next to a million atoms of Cs-135 for a year less than one atom (0.301) would decay and the total energy released would be 13 femtojoules, less than 150 thousandth of the energy released by the caesium-137.

So you have a tradeoff: caesium-135 is less dangerous than caesium-137 but becomes less dangerous more quickly. Both Cs-135 and Cs-137 decay to form stable (non-radioactive) barium so if you can turn a profit selling barium then you’re better off buying a truckload of Cs-137; you’ll be able to sell it as barium sooner.

* It’s worth bearing in mind that nuclear waste eventually becomes safe. Chemical waste from the production of solar cells like silicon tetrafluoride and cadmium telluride remain toxic forever.