Anyone of school age in the UK in the late 20th century will recall August’s hasty ‘back to school’ shop to get new uniform and their new plimsolls for ‘PE’.
Plimsolls were very thin-soled, uncomfortable sports shoes, providing little in the way of padding or arch support. The choice was black or white, sometimes with a laced option, but their primary design brief was to reduce scuffing on polished wooden gym floors. Style and comfort were not required.
They did, however, have one distinctive feature – a dark line running around the rubber bumper, where the sole joined the canvas upper. Any water or mud above that line was a guarantee your socks were sodden.
The line is significant because of its association with shipping safety and has an interesting link to chemical risk assessment.
Victorian “sand shoes”, like those old gym shoes, were popularly known as ‘Plimsolls’. The dark line around the sole was reminiscent of a load line or the ‘Plimsoll line’ on a ship’s hull. This line is critical to a ship’s safety, showing the maximum depth to which it can be safely loaded, including cargo, crew or passengers under defined conditions. The load line applies Archimedean physics to shipping. Loading the ship beyond that line means it sits too low in the water, risking instability, flooding and loss of life, especially in difficult conditions.
The hulls of twelfth-century Venetian ships displayed a simple cross as a load marker. However, Samuel Plimsoll, MP for Derby, UK, campaigned for its wider introduction during the mid-19th century. He and his wife Eliza were appalled by the terrible loss of ships and crews caused by vessels being overloaded with cargo during the maritime trading boom of the Industrial Revolution. Sailors could be imprisoned for refusing to sail on a ship, even if they believed it to be unsafe.
Plimsoll’s early attempts to introduce mandatory safe-load lines met considerable opposition. Many MPs had interests in shipping and overseas trade and were reluctant to support restrictions seeming to limit commercial activity.
Plimsoll published a book and helped prompt a Royal Commission on the issue in the 1870s. Eventually, having caught the public’s attention, his campaigning contributed to the Merchant Shipping Act 1876, UK-wide legislation requiring ships to display load lines to demonstrate safe loading, later known as the ‘Plimsoll line’.
A simple idea: establish a clear boundary to reduce the risk of harm and loss of life. It was gradually adopted by various shipping nations. In 1966, load line rules were standardised internationally through the International Convention on Load Lines, adopted under the auspices of the International Maritime Organization (IMO).
That same thinking is directly relevant to chemical regulation and underpins the work we do at ACRE. The orange sweep across the “A” in ACRE’s logo defines our wider role in helping organisations understand, assess and manage chemical risk. Inspired by the Plimsoll line, it represents the importance of clear limits, proportionate controls and informed decision-making.
As with the Plimsoll line, the underlying principle is straightforward, even if complex science and regulation are behind it. Chemical safety thresholds are intended to protect workers and the most vulnerable in society, as well as our environment.
Why chemical safety limits include built-in caution
These limits also include a significant degree of conservatism – this is not accidental. The uncertainty factors take account of differences in susceptibility, the severity of observed effects and gaps in the available evidence.
The Plimsoll line itself has also developed over time. Ships now display multiple load lines for different maritime and freshwater conditions, reflecting factors such as water density, seasonal changes and the operating environment.
Chemical risk assessment works in a similar way. Different values are derived depending on who or what is being protected, the route and duration of exposure, the nature of the hazard and the level of uncertainty involved.
DNEL vs DMEL vs PNEC: what’s the difference?
In the EU, DNELs, DMELs and PNECs are not simply different names for the same thing; each is derived for a particular purpose and reflects a different protection goal. DNELs are generally used to identify exposure levels below which adverse effects are not expected, DMELs are used where a no-effect threshold cannot be established, and PNECs describe concentrations below which environmental harm is not expected. Other regulatory jurisdictions set ‘safe limits’ with different names, sometimes using different assessment methods and limit-setting processes, but all are effectively doing the same thing.
In short: DNELs, DMELs and PNECs each protect something different – human health where a safe threshold exists, human health where it doesn’t, and the environment – so the right one depends on what’s being assessed.
Industry and regulators may not always agree on the assumptions made, the assessment factors applied or the level of precaution required – that is part of the regulatory discussion. However, the basic principle should be one on which we can all agree: setting and applying appropriate thresholds allows chemicals to be used responsibly while protecting people and the environment.
Whether the line appears on the hull of a ship, around the sole of an old gym shoe or within a chemical safety assessment, its purpose is much the same: to show where safe use ends and unacceptable risk begins.
About the author
Dr Craig Kelly, Director, Senior Consultant: Craig brings his long experience of working in both EU and UK REACH to assist our clients with their decisions, and also includes consortium support. He also brings his expertise in toxicology and ecotoxicology to support clients with technical aspects of their regulatory projects. This includes dossier updates, study quality and technical review, and preparing endpoint summaries and testing plans.
Historical and regulatory details were checked against the following sources, which informed the discussion of the Plimsoll line, Samuel Plimsoll’s campaign, load-line regulation and chemical safety thresholds.
https://heritage.lrfoundation.org.uk/what-is-the-plimsoll-line
https://www.rmg.co.uk/stories/maritime-history/samuel-plimsoll-ship-safety
https://echa.europa.eu/exposure-assessment-and-risk-characterisation-recommendations
