A hazardous substance is a chemical element, compound or mixture that has the potential to cause harm. Both inorganic or organic substances can be harmful. A substance is considered hazardous if it’s poisonous, noxious, toxic, corrosive, flammable, explosive or radioactive. These substances have the potential to not only harm humans and other organisms, but also to cause ecological imbalance.

Erlenmeyer flasks with colorful solution and variety of chemical hazard warning labels

What Are The Warning Signs For Hazardous Substances?

Manufactured hazardous substances are legally required to have labels and symbols that explicitly state that they’re harmful. These are called GHS labels (Globally Harmonized System of Classification and Labelling of Chemicals), and they include easily recognisable pictograms, like the skull and crossbones symbol, which warns of a toxic substance, or a flame, which tells you that the product you’re handling is flammable. 

However, in spite of the rules and regulations surrounding the labelling of dangerous products, there are still many hazardous substances that naturally occur in the environment that can’t be identified by a label or packaging, such as asbestos. Nonetheless, there are always some warning signs that can help you determine whether a substance is hazardous or not. So, using your senses, you should always watch out for the following tell-tale signs:

  • Foul or noxious odour in food: If your food smells unpleasant, it’s most likely the result of bacterial decomposition. It could also indicate the presence of a chemical that’s harmful to the respiratory system. When something decomposes, sulphide compounds are released, and these are responsible for the smell of gone-off food. The decomposition process also releases other dangerous gases, like methane. Ultimately, though, food that has a rancid smell is an indication of bacterial presence, some of which might cause food poisoning or botulism. In a nutshell: don’t eat food that smells bad.
  • Irritating to the skin: Skin can be irritated by a wide range of allergens, but the most dangerous ones are those that can result in anaphylactic shock. In these cases, your internal air passageways can become blocked, and your kidneys and brain may also swell due to the hyper reaction of the immune system. Some plants can produce toxins that are irritating to the skin, such as those produced by poison ivy. But a substance that irritates the skin can also be something corrosive, from hydrochloric acid and household cleaners to certain types of sunscreens.
  • Having a bitter taste: Many types of poison, particularly organic ones, have a bitter taste. Never ingest anything that has a bitter taste if you’re unsure what it is. Of course, some medicines and food or drinks have bitter tastes, so an element of common sense is needed in order to gauge what’s meant to be bitter and what isn’t. In general, never eat berries or fruits if they taste bitter; this is usually Mother Nature’s warning sign.
  • Producing heat when wet: Some chemicals, like bleach, produce heat when they react with water. It’s a good idea to stay away from these chemicals, or, if you’re handling them, to wear the recommended PPE. The same is true for substances with high alkalinity, such as sodium hydroxide. Substances that have high alkalinity are poisonous and corrosive, with the potential to deeply penetrate skin tissue.
  • Bubbling or generating gas: Many types of drinks produce bubbles. While this is normal in the case of carbonated beverages, it becomes a warning sign if the liquid isn’t meant to bubble. For example, if bubbles start to form in milk that has been undisturbed, it could be an indicator of bacterial action.
  • Highly reactive to metals: Acidic substances like sulphuric acid are highly reactive to metals. Hydrogen is liberated as it’s replaced by the metal, generating heat in the process. Any substance that is highly reactive to metal is hazardous because it can burn your skin and can damage your mucous lining.
  • Easily ignites: Many substances ignite if they’re in fine powdered form. For example, coffee creamer can easily be ignited when blown into the air and exposed to an ignition source. This is due to its chemical composition, which is basically very finely ground glucose that contains stored energy and burns very easily. Still, you’d need to expose the coffee creamer to a flame in order to ignite it; it won’t just combust on impact with air. Hazardous flammable substances, on the other hand, like gasoline or gunpowder, are explosive even at room temperature.
  • Fibrous and crumbling: Asbestos is on the Environmental Protection Agency’s (EPA) top 10 most hazardous substances list. Formerly used as fireproof building insulation, this lethal substance is highly carcinogenic and can cause a host of respiratory diseases. Although the use of this substance in building insulation has been banned, some old and dilapidated buildings may still contain asbestos. To identify asbestos, check if your insulation looks fibrous or crumbling, like little pebbles, and if it has a grey-brown or silvery-gold appearance. If it does, it’s worth getting it professionally checked immediately. Do not handle any substance that may contain asbestos if you don’t have the proper protective clothing and equipment.
  • Glowing in the dark or emitting other types of radiation: Radioactive substances emit varying intensities and types of radiation, like X-rays, alpha particles, and gamma rays (and no, you won’t Hulk out if you’re exposed to high levels of gamma rays – your cells will be destroyed). Even if you don’t have a Geiger counter, you can test for radioactivity by exposing a photographic film enclosed in a black envelope to a possible source of radiation.
The Globally Harmonized System of Classification and Labeling of Chemicals vector on white background
Always check the hazard labels of any substance you’re handling

How Do You Control A Hazardous Substance?

Hazardous substances can be found virtually everywhere, even your homes. Handling hazardous substances requires different approaches depending on the type of substance, i.e. whether it’s:

  • Poisonous
  • Noxious
  • Toxic
  • Corrosive
  • Flammable
  • Explosive
  • Radioactive

In most cases, the plastic and sealed containers that these substances come in will have been designed specifically to keep that product safe (or, more accurately perhaps, to keep you safe from the product); and, as we mentioned earlier, these containers will usually include warning labels and safety instructions. That said, it’s always useful to know how to control a hazardous substance:

  • Careful control of the temperature and pressure is important when handling flammable and explosive substances. All possible sources of ignition must be removed from the vicinity of these substances.
  • Special protective clothing and containers are necessary when handling radioactive substances. Similar precautions are necessary when dealing with highly toxic or corrosive substances. Multiple layers of protection are necessary in these cases, and strict compliance to safety protocols must be followed.
  • Transporting large amounts of hazardous materials requires high-level precautions and coordinations. You may need to coordinate with local authorities to ensure the safe transport of hazardous substances. Specialised trailer containers are usually designed for specific types of hazardous substances that are being transported.
Personal protective equipment on white counter
Always wear the relevant PPE when handling hazardous substances

How To Identify A Hazardous Substance

Identifying hazardous substances is relatively easy if there are labels and graphic symbols on their containers. However, in cases where a potentially hazardous substance is unknown, such as in the case of pollution, chemical testing is necessary. Here are some common methods:

  • Testing for the pH level
  • Using a Geiger counter
  • Testing for heavy metals
  • Using spectroscopy
  • Subjecting samples to gas chromatography
  • Adding chemical reagents to test for specific poisons

Carrying out these tests requires expertise in analytical chemistry and a knowledge of how to use laboratory equipment in order to identify unknown samples of potentially hazardous substances. If you’re unable to do this but are concerned about a substance you’re handling, always make sure to take the necessary safety precautions first, or leave it alone and contact a professional. 


All content published on the ReAgent.co.uk blog is for information only. The blog, its authors, and affiliates cannot be held responsible for any accident, injury or damage caused in part or directly from using the information provided. Additionally, we do not recommend using any chemical without reading the Material Safety Data Sheet (MSDS), which can be obtained from the manufacturer. You should also follow any safety advice and precautions listed on the product label. If you have health and safety related questions, visit HSE.gov.uk.