Science: Molecule of the Month: A fuel-enhancing anaesthetic with explosive potential: John Emsley looks at the gas ethyl chloride, a catalyst that requires careful handling

It is 8.30pm on 1 February at Associated Octel's chemical plant in Ellesmere Port, Cheshire. A pressurised reactor vessel begins to leak highly flammable ethyl chloride mixed with corrosive hydrogen chloride gas. The alarm is raised, the emergency services alerted, and the local fire brigade is quickly on the scene. Then, at 10pm, the dreaded event occurs: a spark ignites the ethyl chloride vapour and flames engulf the reactor, which still contains more than 20,000 litres of ethyl chloride under pressure. A major disaster threatens, but thanks to modern chemical plant design there is no devastating fireball. The blaze is brought under control without people being injured or homes put at risk, though it causes severe damage to the plant.

Ethyl chloride, also known as chloroethane, is a gas with an ether-like smell. It condenses to a colourless liquid at 12C and will remain liquid under pressure at much higher temperatures. In vapour form it is twice as dense as air, so that any leakage tends to seep along the ground rather than disperse. It may well have been this which allowed the leaking material to find a source of ignition, perhaps something as tiny as an electrostatic spark.

The Health and Safety Executive (HSE) is investigating the fire, and meanwhile has banned the manufacture of ethyl chloride at Ellesmere Port. 'We have served a prohibition notice on Octel and this will remain in force until we are satisfied that they are taking all necessary precautions to limit the consequences of a release of flammable substances on workers, the environment and those living nearby,' says Mark Wheeler of the HSE.

In 1993 Octel manufactured more than 45,000 tonnes of ethyl chloride by reacting ethylene and hydrogen chloride, with the latter being made on site from chlorine gas. The chlorine is made by passing electricity through a salt solution. Only a year ago the company spent pounds 10m to become the first UK chemical company to make all its chlorine by an environmentally friendly process that does not use mercury. According to Dr John Little, managing director, the new process also cuts energy consumption by 25 per cent and meets the requirements of the Paris Convention, which aims to phase out the mercury process in Europe by 2010.

Octel does not sell much ethyl chloride as such but converts most of it to tetraethyl lead (TEL), the anti-knock additive put into petrol, which it supplies to more than 50 refineries around the world. A little TEL will turn a low-grade fuel into a high-octane one by acting as a catalyst.

The accident at Ellesmere Port demonstrated the importance of modern design and plant layout. When gas under pressure escapes from a ruptured pipe or tank it can lead to spectacular disasters, of which Piper Alpha is the worst example. Octel's ethyl chloride reactor vessel was specially designed to avert such an outcome. According to Brian Swithenbank, company safety officer, it was sheathed in a coating that automatically protects the contents when the tank is engulfed in flames. Gases within the coating cause it to expand, forming an insulating layer that can withstand heat and flames for at least two hours.

Ethyl chloride has other uses as a chemical reagent. At one time it was used to manufacture an early type of sleeping pill called sulphonal. Today it is reacted with wood pulp or cotton to make ethyl cellulose. This is used as a plastic, a coating for paper and wire, a binder for tablets and as a hot-melt adhesive. Ethyl chloride is also used by itself, in local anaesthetic sprays, as a refrigerant and as a speciality solvent for fats, oils, resins and waxes. It is non-toxic and the safe working level in air is as high as 0.1 per cent, although at such concentrations it irritates the eyes.

Ethyl chloride's main outlet is still for manufacturing TEL, although less and less of this is now produced. Lead in petrol interferes with catalytic converters, and is also undesirable for health reasons. However, in the years when most petrol was leaded with TEL, some plants in the US made up to a billion litres of ethyl chloride a year.

Another reason for the decline in production is that it is an organochlorine compound, and some environmentalists are worried about the release of such materials into the atmosphere. However, ethyl chloride poses no threat to the ozone layer because it quickly reacts with oxygen and is carried away by rain. As yet it has not been identified as a natural chemical, though its counterparts, methyl chloride and ethyl bromide, have been discovered in marine algae.

The author is science writer in residence in the Department of Chemistry, Imperial College, London.

Arts & Entertainment
Madonna in her music video for 'Like A Virgin'
music... and other misheard song lyrics
Sport
Steven Gerrard had to be talked into adopting a deeper role by his manager, Brendan Rodgers
sportThe city’s fight for justice after Hillsborough is embodied in Steven Gerrard, who's poised to lead his club to a remarkable triumph
News
Much of the colleges’ land is off-limits to locals in Cambridge, with tight security
educationAnd has the Cambridge I knew turned its back on me?
News
Waitrose will be bringing in more manned tills
newsOverheard in Waitrose: documenting the chatter in 'Britain's poshest supermarket'
VIDEO
News
The energy drink MosKa was banned for containing a heavy dose of the popular erectile dysfunction Levitra
news
Environment
People are buying increasing numbers of plants such as lavender to aid the insects
environmentGardeners rally round the endangered bumblebee
Sport
Australia's Dylan Tombides competes for the ball with Adal Matar of Kuwait during the AFC U-22 Championship Group C match in January
sportDylan Tombides was diagnosed with testicular cancer in 2011
Arts & Entertainment
Customers browse through Vinyl Junkies record shop in Berwick Street, Soho, London
musicBest exclusives coming to an independent record shop near you this Record Store Day
News
Ida Beate Loken has been living at the foot of a mountain since May
newsNorwegian gives up home comforts for a cave
Extras
indybest10 best gardening gloves
Arts & Entertainment
tvIt might all be getting a bit much, but this is still the some of the finest TV ever made, says Grace Dent
Arts & Entertainment
Comedian Lenny Henry is calling for more regulation to support ethnic actors on TV
tvActor and comedian leads campaign against 'lack of diversity' in British television
News
Posted at the end of March, this tweeted photo was a week off the end of their Broadway shows
people
News
peopleStar to remain in hospital for up to 27 days to get over allergic reaction
Arts & Entertainment
The Honesty Policy is a group of anonymous Muslims who believe that the community needs a space to express itself without shame or judgement
music
News
Who makes you happy?
happy listSend your nominations now for the Independent on Sunday Happy List
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Have you tried new the Independent Digital Edition iPad app?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Apprentice IT Technician

£150.00 per week: QA Apprenticeships: This company is a company that specializ...

1st Line Technical Service Desk Analyst IT Apprentice

£153.75 per week: QA Apprenticeships: This company is an innovative outsourcin...

1st Line Helpdesk Engineer Apprentice

£150.00 per week: QA Apprenticeships: This company has been providing on site ...

Sales Associate Apprentice

£150.00 per week: QA Apprenticeships: We've been supplying best of breed peopl...

Day In a Page

How I brokered a peace deal with Robert Mugabe: Roy Agyemang reveals the delicate diplomacy needed to get Zimbabwe’s President to sit down with the BBC

How I brokered a peace deal with Robert Mugabe

Roy Agyemang reveals the delicate diplomacy needed to get Zimbabwe’s President to sit down with the BBC
Video of British Muslims dancing to Pharrell Williams's hit Happy attacked as 'sinful'

British Muslims's Happy video attacked as 'sinful'

The four-minute clip by Honesty Policy has had more than 300,000 hits on YouTube
Church of England-raised Michael Williams describes the unexpected joys in learning about his family's Jewish faith

Michael Williams: Do as I do, not as I pray

Church of England-raised Williams describes the unexpected joys in learning about his family's Jewish faith
A History of the First World War in 100 moments: A visit to the Front Line by the Prime Minister's wife

A History of the First World War in 100 moments

A visit to the Front Line by the Prime Minister's wife
Comedian Jenny Collier: 'Sexism I experienced on stand-up circuit should be extinct'

Jenny Collier: 'Sexism on stand-up circuit should be extinct'

The comedian's appearance at a show on the eve of International Women's Day was cancelled because they had "too many women" on the bill
Cannes Film Festival: Ken Loach and Mike Leigh to fight it out for the Palme d'Or

Cannes Film Festival

Ken Loach and Mike Leigh to fight it out for the Palme d'Or
The concept album makes surprise top ten return with neolithic opus from Jethro Tull's Ian Anderson

The concept album makes surprise top ten return

Neolithic opus from Jethro Tull's Ian Anderson is unexpected success
Lichen is the surprise new ingredient on fine-dining menus, thanks to our love of Scandinavian and Indian cuisines

Lichen is surprise new ingredient on fine-dining menus

Emily Jupp discovers how it can give a unique, smoky flavour to our cooking
10 best baking books

10 best baking books

Planning a spot of baking this bank holiday weekend? From old favourites to new releases, here’s ten cookbooks for you
Jury still out on Manchester City boss Manuel Pellegrini

Jury still out on Pellegrini

Draw with Sunderland raises questions over Manchester City manager's ability to motivate and unify his players
Ben Stokes: 'Punching lockers isn't way forward'

Ben Stokes: 'Punching lockers isn't way forward'

The all-rounder has been hailed as future star after Ashes debut but incident in Caribbean added to doubts about discipline. Jon Culley meets a man looking to control his emotions
Mark Johnston: First £1 million jackpot spurs him on

Mark Johnston: First £1 million jackpot spurs him on

The most prize money ever at an All-Weather race day is up for grabs at Lingfield on Friday, and the record-breaking trainer tells Jon Freeman how times have changed
Ricky Gervais: 'People are waiting for me to fail. If you think it's awful, then just don't watch it'

Ricky Gervais: 'People are waiting for me to fail'

As the second series of his divisive sitcom 'Derek' hits screens, the comedian tells James Rampton why he'll never bow to the critics who habitually circle his work
Mad Men series 7, TV review: The suits are still sharp, but Don Draper has lost his edge

Mad Men returns for a final fling

The suits are still sharp, but Don Draper has lost his edge
Google finds a lift into space will never get off the ground as there is no material strong enough for a cable from Earth into orbit

Google finds a lift into space will never get off the ground

Technology giant’s scientists say there is no material strong enough for a cable from Earth into orbit