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What Are HNS?

3 minute read

Many chemicals transported by sea are considered hazardous and noxious substances that can have significant impacts when spilled into the marine environment.

Marine incidents involving hazardous and noxious substances (HNS) occur at a much lower frequency than oil spills. However, the consequence of a HNS spill can be equal or greater than that of an oil spill. The diverse amount of HNS transported, their varying physical and chemical properties, the uncertainty as to how they may behave in the marine environment and the potential they have to impact human health mean that response to HNS spills can be even more complex than response to oil spills.

What are HNS?

The International Maritime Organization (IMO), a specialized agency of the United Nations responsible for improving the safety and security of international shipping and pollution prevention, define HNS as a substance other than oil which, if introduced into the marine environment, is likely to create hazards to human health, harm living resources and marine life, result in economic or proprietary damages or interfere with other legitimate uses of the sea.

There are approximately 6,500 substances carried by ship, either in bulk or in packages/containers, covered under the IMO’s definition of HNS, under the 2010 HNS Convention. They include substances such as:

    • Chemicals (e.g. chlorine, caustic soda)
    • Refined oil (e.g. aviation fuel, naptha)
    • Acids (e.g. sulphuric acid, battery acid)
    • Fertilizers
    • Alcohols
    • Liquefied natural gas (LNG)
  • Liquefied petroleum gas (LPG)

A general rule is that the substance concerned is likely to be considered HNS if it:

  1. Has a low biodegradation rate or high persistence
  2. Has a high bioaccumulation rate
  3. Is classified as toxic, flammable, explosive, corrosive or reactive

Radioactive and infectious substances are outside of the scope of what is defined as HNS.

How commonly are HNS transported at sea?

It is estimated that over 2,000 varieties of HNS are transported regularly by sea, either in bulk or in packaged form. Chemical tankers trade over 200 million tonnes of HNS products globally on an annual basis. As of 2009, methanol and liquid chemicals accounted for some 46% of these while palm and vegetable oils accounted for 29%; however, the amount of tonnage being traded has been steadily increasing over the past decade.

Why are HNS spills complex?

The greatest challenge facing the response and recovery of HNS spills is the sheer number and variety of substances. In order for responders to be effective in their response strategy the hazard and behaviour of HNS spilt must be known. The human health and safety implications as well as the effects on the environment of the spilt HNS must be carefully considered as HNS may be flammable, explosive, toxic or corrosive. Further, HNS present differing physical properties such as:

These physical properties may also vary depending on the environmental conditions at the time of the spill. Some HNS can evaporate rapidly, dissolve wholly, partly or not at all, float or sink. Their behaviour can also vary over time and depending on water conditions.

How are HNS regulated in Canada?

Because of its inherently international nature, commercial marine shipping is regulated at the international level. The IMO has developed several Conventions and Codes which apply to the safe transport of HNS dependent upon the physical form and quantity of the substances transported. Two of the most significant Conventions governing the transportation of HNS developed by the IMO are the International Convention for the Safety of Life at Sea (SOLAS) and the International Convention for the Prevention of Pollution from Ships (MARPOL). Canada has ratified both SOLAS and MARPOL and enforces the Conventions’ regulations within Canadian territorial waters.

In 2000, the IMO also developed the Protocol on Preparedness, Response and Co-operation to Pollution Incidents by Hazardous and Noxious Substances (OPRC-HNS Protocol). The aim of the OPRC-HNS Protocol is to establish national systems for preparedness and response and to provide a global framework for combating major incidents or threats of marine pollution caused by HNS transported by sea. States which are a party to the OPRC-HNS Protocol are required to establish response plans for handling HNS pollution incidents, either nationally or in co-operation with other countries. Although the OPRC-HNS Protocol came into force in 2007, Canada is not a party to the Protocol at this time.

Learn more from us about what steps Canada is taking to regulate HNS soon.

Learn More:

HNS Spills
Protocol on Preparedness, Response and Co-operation to Pollution Incidents by Hazardous and Noxious Substances (OPRC-HNS Protocol)

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