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Danger Signs in the Laboratory, Workplace and Hospital

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Susan is a science geek and writer who loves writing articles and tutorials to help you out!

What do these signs mean?

What do these signs mean?

Danger Signs

Danger signs indicate the many dangers that are expected in the laboratory, hospital or workplace. It is very important to understand these danger signs so that you will know what they mean and what precautions you need to take.

The common workplace today, especially in the manufacturing, health and medical industries, is teeming with hazards from apparatus to chemicals. Working with these can prove very risky, so it is important to know all the precautions you can take to protect yourself from these dangers

The best way to empower yourself with such knowledge is by checking all the danger signs associated with substances, chemicals and apparatuses in your workplace. This guide fully explains over twenty danger signs that are commonly found all over the world.

Irritant or Harmful

Irritant or Harmful

Irritant or Harmful

This danger sign is perhaps the most common of all because most substances in laboratories and hospitals have this sign. When you see this sign on a substance, it means that the substance may irritate your skin, causing redness and itchiness. If this substance comes in contact with your skin, it could cause

  • A severe redness on the skin.
  • Cracking and dryness.
  • Itchiness.
  • Damage to the eye.

To avoid this, you can take precautionary measures such as wearing gloves, working slower with irritant chemicals and keeping safety goggles on the eyes. These kinds of precautions may seem very obvious but did you know that work-related skin problems are one of the most reported non-injury by workers in the United States? Long-term skin problems can result from repeated short-term contact with irritant chemicals.

If you come in contact with an irritant chemical, wash with cold water immediately to prevent further damage and dilute the chemical.

There are two variations of this sign: irritant or harmful. They both mean the same thing and have the same effects. A sign with a large 'X' and an 'i' in the bottom right corner means irritant whilst the sign without the 'i' means harmful.




This sign can be identified by a large black flame on an orange background. Flammable substances often include chemicals that are not necessarily found in the workplace. Aerosols and other compressed cans can be highly flammable and must be handled with great care.

The flammability of a substance is the degree of difficulty required for a substance to combust. This degree is found through fire testing and the result is documented in many safety codes and government regulations. The standard grades of flammability can be found in the table below.

Flammable substances catch aflame very easily under normal conditions. Compared to other substances, they can start a fire much quicker than those that don't have this sign. To precaution yourself, follow your workplace's instructions as there are specific rules associated with various workplaces.

This list shows some common highly flammable substances (it is not exhaustive). These include the following:

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  • Rubber
  • Ethanol (Alcohol)
  • Methanol
  • Wood
  • Gasoline (Petrol)
  • Acetone (found in nail polish remover)

Categories of Flammability

CategoryEasy or Difficult to Ignite?Examples


100% non-combustible, material will never burn

Water, Carbon Dioxide (used in fire extinguishers)


Needs to be pre-heated to burn

Cooking oils, lubricating oils


Difficult to ignite



Will ignite under any temperature conditions

Ethanol, acetone


Substance needs to be dispersed in air and rapidly vapourizes at normal atmospheric pressure

Natural gas, butane, propane




A substance that is corrosive will burn human skin very severely and will destroy any material that comes in contact with it. These substances may even corrode metal.

The word corrosive derives from the Latin word "corrodere" which means "to gnaw." This derivative fits the word perfectly as it gnaws or destroys anything in its path. To protect yourself from corrosive substances, always make sure that you check for this danger sign on all substance labelling. Wear gloves, a face mask, eye goggles and a laboratory coat to protect yourself from corrosive substances.

Many people confuse acids and bases by saying that just acids are corrosive and that bases are not. This is not true and must not be confused! Both acids and bases are corrosive, this can be seen on the pH scale.

List of Corrosive Substances

The list below refers to substances that are labelled as corrosive. (It is not an exhaustive list!) Make sure to keep an eye out for these especially in the laboratory!

  • Strong acids – Nitric acid, hydrochloric acid, sulphuric acid (found in car batteries).
  • Super acids – These are extremely strong acids that are not very common.
  • Concentrated acids with a higher pH – for example, acetic acid or formic acid.
  • Strong bases, alkalis or caustics – for example, sodium hydroxide (used in soap).
  • Hydrogen peroxide.

You should consult Material Data Safety Sheets for more information on the specific corrosive substance you are referring to. This sheet should give you detailed information on all danger signs associated with it.

Dangerous to Environment

Dangerous to Environment

Dangerous to Environment

This sign means that this substance will cause damage to the environment such as fish, aquatic species and natural organisms. For example, if you throw a substance with this danger sign in the water, it could kill fish and other species which are living in the water.

Always make sure to dispose of these chemicals carefully and mindfully, knowing that any contact with the outside world could cause damage. Your local council may be able to dispose of these substances safely for you, simply ask to see if it is possible.




If you ingest, inhale or otherwise make contact with these substances, they can cause serious damage from serious injury to instant death.

To precaution yourself against these chemicals, do not in any circumstances ingest or inhale these substances. Doing so could damage your internal organs, respiratory system or result in death. Wear all relevant safety equipment and make sure to check the Material Data Safety Sheets of all chemicals you are using.




An explosive substance is not commonly found in the workplace or laboratory simply because of the huge danger it poses. These substances have masses of energy to exert and any shock to the chemical can release this energy. That equals an explosion.

Keep these substances away from heat, fire and never drop or exert pressure on them. Because of their huge danger, it is advised to work under the supervision of a safety instructor when handling these.




An oxidizing substance is one that releases large amounts of heat when it comes in contact with other substances. These substances do not pose much danger by themselves but pay particular attention when mixing chemicals together, or getting them involved in a chemical reaction. This is when the oxidation kicks in – releasing much heat.

When you see a substance labelled with this sign, what do you do? Firstly, wear all relevant safety equipment (especially gloves for hand protection, as the oxidizing substance may react causing much heat to the hands) and make sure to have a fire blanket available in the workplace. Check a Material Data Safety Sheet for more information on what specific chemicals will fulfill the oxidizing reaction with the chemical you are checking.

Always be careful when reacting an oxidizing chemical and a flammable chemical together – it could lead to a fire.




As the name suggests, a biohazard is a living organism or tissue which poses a danger to humans if they come in contact with it. You may catch a contagious disease by coming in contact with the substance, or get a virus.

These biological organisms come in a range of shapes and sizes from viruses to living tissue to contagious microorganisms to harmful bacteria. Biohazards are most commonly found in hospitals and in biological laboratories, especially clinical laboratories which deal with human tissue and blood samples on a daily basis.

Always wear a face mask, lab coat, eye goggles and gloves to fully shield yourself from the substance. Don't come in contact with it unless you truly need to – do so whilst following all safety procedures. Dispose of hypodermic needles in a sharps container, you will notice that there will be a biohazard sign on the front of the box.

High Voltage

High Voltage

High Voltage

This sign indicates high voltage, at such a high level that it could cause death. This sign is mainly found in industrial workplaces where high power is needed. Keep away from areas with this sign as it means that electricity is flowing at high voltage through the area. It is debated how much "high voltage" is considered to be, the IET finds that it is 1000 Volts whilst others say 35,000 volts (on electric transmission sites).

Protect yourself by wearing extra clothing that insulates rather than conducts. Stay away from all areas with this sign!

Prohibition Signs

Prohibition signs are commonly found on construction sites that have loud noise, flammable substances on sight and toxic fumes. These signs prohibit you to do certain tasks. Let's take a look at some of them.

  • No Open Flames
  • Non-Drinking Water
  • Do Not Enter
  • Do Not Eat or Drink
  • Do Not Touch

Further Expert Advice on Safety Signs and Symbols

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2014 Susan W


Susan W (author) from The British Isles, Europe on August 02, 2014:

Flourish - Thanks for sharing your experience and thoughtful insight. I totally agree that people should check MSDSs for the chemicals that they are dealing with. I find them very useful when dealing with chemicals in the lab for detailing specific safety precautions and so forth.

People usually laugh when they read these kinds of hubs, because not that many people deal with chemicals on a daily basis. But even simple household chemicals can pose threats. Weak acids such as lemon juice and vinegar can cause permanent damage to the cornea in the eye, if not treated. You are so right, the stuff in those sheets really do surprise you!

FlourishAnyway from USA on August 02, 2014:

With my husband being a chemical engineer and in sales, we have all kinds of industrial chemicals with some of these nifty labels FedExed to the house. Of course, I make him take them elsewhere ASAP. This is a helpful hub. People should consult their MSDS if they have questions on what they're dealing with. Some of the stuff in those MSDSs even for common household chemicals might surprise you.

Susan W (author) from The British Isles, Europe on August 02, 2014:

Laila - Wow, thanks for sharing your experiences in the lab. It seems that without being cautious, the lab can be a very dangerous place. I'm so glad that nothing severe happened with the hydrobromic acid, that doesn't sound like the best thing to happen in a lab! I gained more insight into lab dangers with your comment, so thank you very much! :)

Susan W (author) from The British Isles, Europe on August 02, 2014:

Amanda - I'm so glad that this hub explained some of the signs you didn't know. Whilst some are self-explanatory, there are a few that can be hard to guess (such as biohazard). Thanks for following me too, I really appreciate it! Great to see you are on the HubChallenge too.

Susan W (author) from The British Isles, Europe on August 02, 2014:

John - Thanks for reading this hub and for the great comments. :-) Always appreciated. Yes, I agree. Most signs are very self-explanatory and they are designed for easy understanding. For me, the hardest one to guess is the biohazard sign. But once you know what it means, it is easy to recall.

LailaK from Atlanta, Georgia on August 01, 2014:

In my organic chemistry lab, I can't tell you how many times we had our skin irritate and itch, but we still ignored all these danger signs. Once my lab partner braught the hydrobromic acid bottle uncovered (when he wasn't supposed to) and I accidentally ended up inhaling it and felt like I was suffocating for a couple of minutes after that. Great hub! Voted up!

Amanda Brumbelow from Camas, WA on August 01, 2014:

Great hub! I didn't recognize some of these signs. Thanks for writing such a great hub.

John Hansen from Gondwana Land on August 01, 2014:

Interesting and helpful hub Susi. I had only seen a few of these signs before, but at least most are self-explanatory. The pictures in most cases reflect the danger well. Thanks for sharing.

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