September 19 to 25 is the UK’s sixth annual Gas Safety Week, with many firms signing up to publicise the dangers associated with ordinary gas appliances, including deadly leaks of carbon monoxide (CO). However, carbon dioxide (CO₂) also poses a significant industrial hazard, proving that life-giving carbon really isn’t always the good guy. Jon Herbert reports.

Gas Safety Week brings together more than 4000 companies to proactively warn the public and other gas-fired appliance users about not only the combustion and explosive dangers of natural gas, but also the hazards of invisible, colourless, tasteless, odourless CO — the “silent killer”. It is also a timely moment to consider the toxic dangers of CO₂, essential to many manufacturing industries.

Although it is essential to all life on earth as an element, carbon as a gas gets a bad press these days. CO₂ is the main greenhouse gas released to atmosphere from human homes and workplaces and the major culprit of man-made global warming. However, CO₂, and its relative with one less oxygen atom, CO, can pose much more immediate fatal risks.

Gas Safety Week

The news headlines are a grim reminder of how devastating and complex appliance faults and gas leaks can be.

In February this year, an explosion attributed to a gas leak razed a Yorkshire home to the ground, killing the sole occupant. Subsequent investigations further linked the accident to waterlogged ground. It is thought that a copper pipe installed correctly in the early 1970s corroded and fractured over time at a point where two concrete floor slabs had moved because of wet weather. The result was an uncontrolled gas leak. No health and safety laws were breached.

In April, the roof of a Birmingham home was blown off by a gas explosion, with the rest of the property reduced to “basically rubble”, according to police reports. The explosion was deemed an accident, due to gas ignited by a naked flame. One man was seriously hurt and three other houses were affected by the blast.

The 2016 Gas Safety Week is an awareness campaign aimed primarily at households and landlords. It warns of the risks of gas leaks, fires, explosions, along with CO poisoning.

As the organiser, the Gas Safe Register points out gas safety is an all year round priority; gas appliances should be checked annually by a qualified Gas Safe registered engineer.

Heating installers are expected to be at the forefront of the sixth safety week which is supported by organisations as diverse as NHS Choices, the RNLI, construction contractor Carillion, the City of Stoke-on-Trent, the defence technology company QinetiQ, plus SSE, British Gas and many constituency MPs.

Carbon monoxide

CO is a colourless, odourless, tasteless gas, produced from an incomplete combustion of fuel — when a gas appliance is not functioning correctly.

Once in the respiratory system, CO forms a long-lasting bond with haemoglobin in the blood stream at the expense of life-supporting oxygen molecules. It can be fatal and long-term effects include psychological and neurological damage.

The six signs of CO poisoning are: headaches, dizziness, breathlessness, nausea, collapse and loss of consciousness. Lazy yellow flames, rather than crisp blues ones, black marks or stains on or around appliances, and excessive room condensation are also vital tell-tales of CO leaks.

Fitting audible CO alarms is strongly recommended.

The threat from low CO levels is most serious for people suffering from heart diseases like angina and clogged arteries, or congestive heart failure. A single exposure can cause chest pain and reduce the ability to exercise.

One oxygen molecule more: carbon dioxide

CO₂ is also a product of combustion. Although its main appearance in most premises is probably in bottles of fizzy drink, CO₂ is common in many industries: as an inert gas in welding, a pressurising gas in air guns, a chemical feedstock, a solvent in the decaffeination of coffee and in freeze drying. The frozen solid form of CO₂ is used as a refrigerant and an abrasive in dry ice blasting.

Wherever it is used in a workplace environment, a clear understanding of the gas’ effects on the human body, and robust monitoring and detection devices are vital.

Atmospheric levels of CO₂ are 0.037%. Like CO, CO₂ cannot be seen, tasted or smelt. Being heavier than air, it easily forms invisible pockets near to floors and in trenches, tanks, silos and basements. Pockets are an increased hazard when leaking CO₂ is colder than surrounding air.

While excessive CO₂ in the respiratory system stimulates a natural gagging reaction causing us to breathe more deeply, it can be fatal in two ways.

The first is asphyxiation when CO₂ displaces oxygen in the air. However, measuring oxygen levels alone is not an accurate detection method because CO₂ can be toxic in very small quantities — as low as 0.5% by volume. Concentrations above 10% are fatal.

The second element is that when a CO₂ leak occurs, it displaces four times more nitrogen in the air than oxygen. So, it is possible to inhale both near-normal oxygen levels, plus deadly quantities of CO₂.

Like CO, CO₂ bonds with the blood in place of oxygen. Too much CO₂ causes blood to become acidic, affecting the heart.

Health Protection England has issued guidance as to the obvious symptoms associated with various concentrations of CO₂. It advises that a 2% concentration will cause headaches and laboured breathing. Headaches, shortness of breath, dizziness, confusion and respiratory distress will result from 5%. Difficult breathing, vomiting, hypertension and possible fatality arise from a 10% exposure. CO₂ levels of 20% to 30%, or above, will cause convulsions and coma within just five minutes.

Exposure limits

In the UK, CO₂ is classed as a “substance hazardous to health” under the Control of Substances Hazardous to Health Regulations 2002 (COSHH). The HSE publication EH40 Workplace Exposure Limits outlines workplace exposure limits (WELs). WELs are limits to airborne concentrations of hazardous substances in the workplace and are set to help protect the health of workers.

Two ways of defining exposure limits are used and have slightly different implications. The first is the short-term exposure limit (STEL) which is a maximum concentration of between 1.5% (15,000 ppm) and 3.0% (30,000 ppm) by volume over a 15-minute reference period.

The second is the long-term exposure limit (LTEL) calculated at levels of 0.5% (5000 ppm) over an eight-hour reference period. Time weighted averages are the result and are akin to WELs.

Long-term exposure can include short periods of higher than average limits providing they do not exceed the short-term limits.

Safeguards

Meeting occupational exposure limits requires monitoring the actual CO₂ exposure levels of individual employees.

Personal monitoring devices set to measure long-term exposure averages are usually designed to ignore short-term spikes and false alarms.

A second layer of protection can be provided by staff wearing personal breathing detectors that sample the air they are actually breathing. The two caveats here are that detectors must be in the so-called breathing zone — on lapels, collars and top pockets, but not waist belts or low pockets. Light, compact detectors are now available designed to be worn comfortably with freedom of movement.

Another factor worth keeping in mind with practical CO₂ detectors is that in noisy workplaces, strong audible and visual signals are likely to work best.

Published by Croner-i on 16 September 2016