Understanding the risks will help your students practise chemistry safely – and apply those lessons to life too

Why are so many people scared of flying but are happy to cross the road when the number of deaths caused by road accidents is much greater than those caused by air accidents? It is estimated that the probability of dying in a plane crash is 1 in 11 million; it is 1 in 5000 for dying in a car crash.

Why are so many people scared of flying but are happy to cross the road when the number of deaths caused by road accidents is much greater than those caused by air accidents? It is estimated that the probability of dying in a plane crash is 1 in 11 million; it is 1 in 5000 for dying in a car crash (childanxiety.net).

Why do people worry about having radiation therapy but they’re quite happy to lie in the sun or use a sunbed when radiation therapy can treat cancer while sunbathing can cause skin cancer? Even one sunbed session can increase your risk of developing squamous cell skin cancer by 67%, basal cell skin cancer by 29%, and the risk of melanoma increases by 20%.

Why do people worry about having radiation therapy but they’re quite happy to lie in the sun or use a sunbed when radiation therapy can treat cancer while sunbathing can cause skin cancer? Even one sunbed session can increase your risk of developing squamous cell skin cancer by 67%, basal cell skin cancer by 29%, and the risk of melanoma increases by 20% (bit.ly/2Dw04Tj).

The answers to these questions lie in the findings of the report to the Royal Society, Risk analysis, perception and management (1992). The report finds that:

People are more likely to take risks when:

• they are in control;
• the activity is voluntary;
• the risk is easily reduced; and
• there is a low risk to future generations.

People tend to dread things and therefore are not so willing to take risks when:

• things are out of their control;
• many people can be affected; and
• there is a higher risk to future generations.

So what are the implications for teaching health, safety and risk in the school laboratory?

On many occasions when meeting with teachers and technicians I hear phrases such as ‘You can’t do that experiment. It’s too dangerous’; ‘That chemical is banned, so we don’t do that practical activity any more’; ‘I’m nervous that it might go wrong so I don’t do cracking or the alkali metals. I will put on a video instead.’

In reality, as long as teachers and students are confident with handling the apparatus and they have considered the risks involved (ie done a risk assessment), then most practical activities can be carried out safely in the lab. The Gatsby Good Practical Science project provides a framework for delivering good practical science in schools. Benchmark 9 of the framework about taking ‘a balanced approach to risk’ states that students’ experience of practical science should not be restricted by unnecessary risk aversion. In other words schools should not shy away from practical chemistry. There is plenty of guidance and support about this benchmark, including risk assessment and modelling health and safety, available.

In reality, as long as teachers and students are confident with handling the apparatus and they have considered the risks involved (ie done a risk assessment), then most practical activities can be carried out safely in the lab. The Gatsby Good Practical Science project (bit.ly/2gfcphX) provides a framework for delivering good practical science in schools. Benchmark 9 of the framework about taking ‘a balanced approach to risk’ states that student’s experience of practical science should not be restricted by unnecessary risk aversion. In other words schools should not shy away from practical chemistry. There is plenty of guidance and support about this benchmark, including risk assessment and modelling health and safety, available.

Teaching students about health, safety and risk is an important part of the chemistry curriculum. A good starting place is to ask students to think about and discuss the hazards and risks t in everyday life. Then move on to more specific safety issues met in science. Activities such as Our perception of risk and the Risk and dread exercise in the Royal Society of Chemistry’s book Health, safety and risk promote such discussion.

Learning to carry out a risk-benefit analysis will help students to make balanced decisions about wider questions in society such as the use of food additives, parabens in cosmetics or nanoparticles.

### Progression in teaching about health, safety and risk

When students start secondary school, many begin their secondary science learning with a series of lessons on health, safety and lab rules. The recent article Health, safety and apparatus outlines what 11–14 year old students need to know and provides some lesson ideas for teaching this topic. Teaching about risk and the safe handling of equipment at 14–16 (see table below) goes much further than lab rules and routines; it’s about students being able to choose the right equipment, understanding and putting into practice a risk assessment and being able to make sensible decisions in the laboratory. It is also about being able to evaluate risks and make informed choices in wider society.

When students start secondary school, many begin their secondary science learning with a series of lessons on health, safety and lab rules. The recent article Health, safety and apparatus (rsc.li/2T4JCP4) outlines what 11–14 year old students need to know and provides some lesson ideas for teaching this topic. Teaching about risk and the safe handling of equipment at 14–16 (see table 1) goes much further than lab rules and routines; it’s about students being able to choose the right equipment, understanding and putting into practice a risk assessment and being able to make sensible decisions in the laboratory. It is also about being able to evaluate risks and make informed choices in wider society.

### 11–14

• Experimental skills and investigations: use appropriate techniques, apparatus and materials during fieldwork and laboratory work, paying attention to health and safety.
• Scientific attitudes: evaluate risks.

### 14–16

• Experimental skills and strategies: carrying out experiments appropriately, having due regard to the correct manipulation of apparatus, the accuracy of measurements and health and safety considerations, eg suggest methods of reducing risk of harm in the practical situation.
• Required practical apparatus and techniques for chemistry: safe use of appropriate heating devices and techniques, including use of a Bunsen burner and a water bath or electric heater; safe use of a range of equipment to purify and/or separate chemical mixtures; safe use and careful handling of gases, liquids and solids.
• Evaluate risks both in practical science and the wider societal context, including perception of risk in relation to data and consequences. Give examples to show that there are hazards associated with science-based technologies which have to be considered alongside the benefits. Suggest reasons why the perception of risk is often very different from the measured risk (eg voluntary v imposed risks, familiar v unfamiliar risks, visible v invisible hazards).

### 16–18

• Criteria for practical competency at A-level: safely uses a range of practical equipment and materials. (a) Identifies hazards and assesses risks associated with those hazards, making safety adjustments as necessary, when carrying out experimental techniques and procedures in the lab or field. (b) Uses appropriate safety equipment and approaches to minimise risks with minimal prompting.
• Scientific attitudes: consider applications and implications of science and evaluate their associated benefits and risks, eg the benefits and risks to society of using commercial electrochemical cells.

### Safe heating of chemicals

Heating is a key part of practical chemistry as many chemical reactions depend on heating to overcome the activation energy required to get the reaction started. There are several ways of heating chemicals including the use of Bunsen burners, water baths and electric heaters. Table 1 lists some questions to ask and things to think about when planning an experiment that involves heating.

Table 1 Questions to ask when planning an experiment that requires heating

QuestionsThings to consider

What personal precautions should be taken?

Safety glasses or goggles?

Tie long hair back.

Clear working space.

Stand or sit?

What are the risks associated with each method of heating: Bunsen burners, water baths, electric heaters?

Where you are doing the experiment: easy access to gas or electricity?

If using a Bunsen flame, how do you control the size of the flame so that the clamp doesn’t catch fire?

What temperature is needed for the reaction to work?

Use a water bath if the temperature is below 100oC.

Is it within the temperature range of an electrical heater?

Are any of the reactants or products flammable?

Avoid using a Bunsen burner near flammable substances, eg ethanol as this reduces the risk of them catching fire.

If the reaction gets too hot will any harmful by-products be made?

How to control the temperature so it doesn’t get too hot?

How do you avoid the reaction boiling over or shooting out of the reaction vessel?

Reduce temperature of heater or the size of the Bunsen flame.

Use anti-bumping granules

Think about the size of the heating vessel.

Can the experiment be done on a microscale?

Smaller quantities of chemicals are needed.

Spirit burners can be used for heating.

#### The preparation of copper sulfate crystals

Practical problems encountered during the preparation of copper sulfate

On first appearance preparing copper sulfate crystals in the lab is a straightforward practical activity that most secondary students will do at some point in their school careers. However, a high number of accidents and incidents are reported with this experiment – and they are usually down to heating

The practical problems encountered with this experiment are clearly shown in the video Demonstrating chemistry: Top of the flops (20.39 minutes) and those associated with heating summarised opposite. You can get further guidance on this method from CLEAPSS. This involves using a water bath in the first stage, replacing the evaporation basin with a conical flask and adding a couple of anti-bumping crystals. This provides practical solutions to the practical problems summarised opposite. Alternatively the microscale preparation of hydrated copper sulfate crystals uses small quantities of chemicals, replaces the Bunsen burner with a sand tray on an electrical heater and produces good quality crystals without the risks previously discussed.

### Safe handling of glassware

Many chemical reactions are carried out in glassware. Glass needs to be handled carefully. It is brittle and breaks easily if it is dropped, rolls off the bench or is clamped too tightly. It fractures and shatters if subjected to heat shock, ie large sudden changes in temperature such as those that occur during a freeze–thaw reaction or suck-back of cold water into a hot reaction vessel. This principle can be easily demonstrated by heating the end of a thin glass rod in a Bunsen flame until it starts to glow then plunging it into a large trough of cold water.

Finally, glass will ‘flow’ if it is heated strongly. Glassblowers make use of this property as they craft a piece of glass into laboratory apparatus or beautiful ornaments. However, it can also cause difficulties if chemicals are strongly heated in cheap glass boiling tubes. A better alternative are the more expensive, tougher borosilicate glass (Pyrex) boiling tubes.

Students needs to be aware of these properties and of the consequences. When introducing a class practical or demonstrating an experiment it is good practice to discuss what could go wrong and the possible consequences. Students will learn about the hazards and know how to reduce the risk, so they can carry out experiments safely.

Learning about the safe handling of glassware is an important part of developing students’ practical skills and as teachers we should not assume that our students are aware of the hazards. Students are more likely to take note and feel more confident to carry out the practical activity when they understand both the reasons behind and the consequences of practical instructions. They will feel more in control of the situation and know how to reduce the risk of things going wrong.

### More resources

From Learn Chemistry:

Should we worry about … series, for example:

• Food additives and E numbers – rsc.li/2R9I4Bt
• Parabens – rsc.li/2WeIbiV
• Nanomaterials – rsc.li/2sG2mZP

Reacting copper(III) oxide with sulfuric acid – rsc.li/2RdExCm

Cracking hydrocarbons – rsc.li/1pBB7vL

Thermal decomposition of metal carbonates – rsc.li/2B3oxxv

From STEM Learning: Demonstarting chemistry: Top of the flops video – bit.ly/2RbgzHO

From CLEAPSS: Copper sulfate microscale video – bit.ly/2MvwK1Z

### Example: Suck-back

In experiments such as the cracking of hydrocarbons or the thermal decomposition of metal carbonates where carbon dioxide gas is bubbled into limewater, there is always the risk of suck-back. Suck-back can occur when either no more gas is produced or the heat is removed from the reaction vessel. This is because a mini-vacuum is created in the system causing cold water from the trough or limewater from the test tube to be sucked up into the delivery tube until it eventually reaches the hot reaction tube (see figures). The effects of suck-back can be dangerous; the cracking or shattering of the reaction vessel can send pieces of glass flying, spilling hot chemicals. The video Demonstrating chemistry: Top of the flops (2.44 minutes) shows what can happen when suck-back occurs during these experiments.

To minimise the risk of suck-back lift the delivery tube out of the water/limewater just before, or as soon as, heating is stopped. Always make sure that a borosilicate glass boiling tube is used as this is less likely to shatter in the case of suck-back occurring.