Guidance

PRISM: Narrative style risk assessment – non-compliant portable juice blender

Published 10 October 2024

Applies to England, Scotland and Wales

1) The product

The product is a portable cordless USB-C port rechargeable battery juice blender which has multiple hazards identified after testing. It is not supplied with an AC-DC adaptor to charge the product.

First, it is not fitted with an interlock safety feature as detailed within the standard BS EN 60335-2-14. ^{[footnote 1]} This means the product can be accidentally turned on when the blades are exposed, the blades have a rotational speed of 18,000 rpm, and this occurred accidentally at the test laboratory. Second, the blades have been reported to break and detach from the base whilst in use causing the blades to be present in the bottle with the contents of drink. Thirdly, the internal build quality was considered poor as the lithium-ion battery pack, printed circuit board (PCB) and motor were not secure in the base enclosure and the vibration of use or portable nature of the product could lead to risks of a short circuit leading to the possibility of overheating and burns. Finally, the product does not come with user instructions, which could lead to unintended misuse of the product, for example an incorrect charging cable, or AC-DC adaptor could be used which when combined with the poor build quality could damage the battery management system (BMS) which could result in the product being over-charged and causing a fire.

The portable juice blender is marketed at people on the go who would want to create drinks, for example smoothies or protein shakes at home, in the gym, in the car, or at work, as the ingredients are blended directly into the bottle. The user is then required to turn the product upside down to unscrew the drink bottle, so the contents do not spill. Once the drink bottle part is removed the blades are exposed. The user can then drink directly from the bottle immediately after blending.

As the product does not come with an AC-DC adaptor, it does not fall within the voltage limits of The Electrical Equipment (Safety) Regulations 2016, ^{[footnote 2]} therefore this product falls under the scope of The General Product Safety Regulations 2005.

Note: As this is a worked example further product details are not provided here, but would normally include:

• manufacturer/brand
• model
• batch numbers and any other coding
• quantities supplied and over what time period
• how the matter came to the attention of the market surveillance authority (e.g. complaint, intelligence or ports and borders work)
• details of any reported incidents or injuries
• photographs of the product and packaging that, where possible, capture the hazard and identify the product

2) The hazards

There are multiple hazards under assessment. The product was subject to testing by a competent laboratory, with the following assessment scope:

External build quality

The external build quality of the product was found to have the following issues:

It was possible to activate the blade of the unit when the bottle was removed by pressing the power button twice, which causes a cutting hazard. There was no interlock to prevent this as it had no sensor to detect if the bottle was present. This occurred at the test laboratory by accident and is considered dangerous. It is considered that size and design of the blades would probably prevent serious injury, but it would cut the skin.

Internal build quality

The internal components were accessed by removing screws on the base of the product. The internal build quality was considered to be poor as the lithium-ion battery pack was not secured to the enclosure, which could lead to a short circuit, overheating or fire risk, due to the portable and high vibration nature of the product. The connections to the PCB and motor were also only connected by solder, two forms of connection e.g., solder and mechanical fixing should be used to ensure that the connections are secure.

There were no electrical or identification markings (aside from the manufacturer) on the battery pack, which suggested that it may not hold suitable approval – this should be verified with the manufacturer.

The product was not supplied with an instruction manual or warnings, and does not carry essential markings, either CE or UKCA which could indicate a lack of due diligence by the manufacturer. The product is also not marked with a UK importer/manufacturer’s postal details or nominal voltage.

There are multiple primary actual or potential routes to injury for this product:

1. The risk presented by a product which can be accidently turned on with the blades exposed.
2. The risk presented by blades which can break, detach and be found in the drink bottle.
3. The risk with the poor internal construction which could lead to a short circuit and overheating of external surfaces.
4. The risk in which the lithium-ion battery could be overcharged and cause a fire, for example by not using the proper charging cable or capacity source which may cause the battery to charge quicker than intended or capable and might damage the BMS.

Finally, it must be acknowledged that there are a number of unknowns relating to the product’s design and construction which are flagged for further investigation on the basis of a lack of instructions, warnings or marking in relation to design risk management. Understanding the premarket risk considerations, as well as production control are important. The sample product may not be representative of the whole batch in terms of design, production or specification, and some products may have additional or different hazards. This is relevant to the risk evaluation.

3) Who could be harmed?

The people most at risk of harm are any person who interacts with the product in a way where they touch it can potentially be harmed due to contact with the exposed blades. Anyone in the vicinity of the product if the product catches fire, particularly as this product is intended to be portable and as a result could be used within a variety of locations such as the home, or a gym, or left in a car, where a fire starting in the product could combust nearby materials.

4) Harm scenario and severity of harm

From the evidence supplied and the test report, there are multiple hazards with this product, therefore the multiple harm scenario generator can be considered for use. A product deemed to have ‘multiple hazards’ should consider combining the probabilities of the multiple hazards. The hazards should be of a similar level of concern to defend combine the hazards to reach a product risk, compared to using one hazard to convey the product risk.

Scenario 1

The product can be turned on with the blades exposed, as identified within the test laboratory. It is considered by the test house that the size and design of the blades would probably prevent a severe injury, but it is suggested that it could cut the skin.

This scenario can foreseeably result in a level 2 injury. In addition to the note from the test house regarding the blade design and foreseeable injury level, there are also articles ^{[footnote 3] [footnote 4]} which reference injury severity reported from people with experience of cuts from these types of products.

Steps leading to harm

Step 1: The blender is used to make a drink directly into the detachable bottle. The user removes the bottle part which leaves the blender blades exposed.

Step 2: The user does not immediately attach the blade guides for storage or transportation, these could have been lost or thrown away after purchase.

Step 3: The user accidently pushes the power button twice causing the blades to rotate.

Step 4: The user comes into contact with the blades which cause cuts and nerve damage to the hand. A level 2 injury occurs.

Scenario 2

The next scenario describes as reported, that the blades used in the product can easily break and detach from the base. As part of the products design, these blades are then in the bottle which the user would drink from.

This scenario can foreseeably result in a level 2 injury due to the blades breaking at the base as one piece, and due to normal drinking, eating and swallowing motions performed by people it is not realistically foreseen that the blades would be swallowed, and the injury level would be higher.

Steps leading to harm

Step 1: The blender is used to make a drink directly into the detachable bottle, due to the weakness of the blade attachment the blades break off and detach at the base.

Step 2: The user removes the bottle part and does not notice that the blades are broken or missing from the base and in the drink bottle, they drink directly from the bottle.

Step 3: The blades enter the mouth through a natural drinking motion and behaviour, the user sustains substantial cuts to their lips or mouth. A level 2 injury occurs.

Scenario 3

This scenario is that the PCB and motor are only connected by solder which is not sufficient and can fail over time with vibration and movement. In addition, the lithium-ion battery pack is not secured to the enclosure. These could cause a short circuit and overheating, whilst plugged in or unplugged and operating on battery and the product is being used. As the product is in use for this scenario to be likely, it is foreseen someone would be present at the time the product fails.

This scenario can foreseeably result in a level 2 injury.

Steps leading to harm

Step 1: The connection of the internal PCB, motor and lithium-ion battery pack (which contains one cell) fails over time due to vibration of the motor when in use, or when the product is transported due to its portable nature.

Step 2: Internal parts short circuit due to parts becoming loose and touching each other, whilst the product is plugged in and in use. The product can then overheat and cause a burn hazard.

Step 3: It if foreseen that the product is in use or immediately after when the parts become loose, therefore quick intervention due to supervision of the product may take place. The product overheats which causes external surfaces to heat up. The user’s automatic reaction is to pick up the product and throw it outside or away from other nearby materials, however if the product overheats these situations happen quickly and there may be insufficient time to remove the product from the location. This results in burns which cover the arms, torso and some of the face which determine approximately 20% of the total body surface. A level 2 injury occurs.

Scenario 4

The final scenario is that due to the lack of instructions, the user does not use a correct AC-DC adaptor intended to properly charge the product. The product has a USB charging cable intended to connect to a 5V dc supply at a maximum current of 0.5A.

Generic chargers are widely available and are often supplied with universal adapters meaning they can be easily used, therefore it is plausible that the consumer could use a higher capacity source charger, for example a quick charge adaptor, or in-built USB port car charger which are commonly 2-3A as there are no instructions which warns against this. As such the targeted range of voltage and current for the required specified duration of time is not applied which subsequently damages the battery management system (BMS) components causing the battery pack to overcharge and overheat. Critical components in the BMS are designed with specific voltage and current ratings. Operating them above these ratings is likely to result in damage and may render the BMS unable to monitor or to intervene.

An inadequate BMS may fail to detect and prevent an over-charge condition from occurring which may result in the battery cell exceeding its maximum safe charge and could result in thermal runaway. Thermal runaway ^{[footnote 5]} happens to individual battery cells contained within a battery pack when the battery cell temperatures reach a critical point at which exothermic reactions occur. Exothermic reactions are chemical reactions that generate heat faster that it can be dissipated within the battery cell. This heating creates gas inside the battery cell which will eventually cause the cell casing to rupture (known as venting) resulting in release of flammable and potentially toxic gasses. Battery cells in thermal runaway may heat adjacent battery cells if these are within the battery pack sending these cells into thermal runaway too, creating a cascade event. This product has one cell within the battery pack, however batteries in thermal runaway can produce a rapidly developing and very aggressive fire which can cause serious harm to persons and cause a lot of damage.

It could be hypothesised that the product is unattended as it is being charged either before or after use, overnight, or that due to the portable nature of the product it is not in the usual kitchen area of a domestic home which may have more harmful implications if there is a lack of a smoke alarm to warn the user or if the product is being charged while occupants are asleep. Thermal runaway can happen quickly and may not allow the user time to react.

This scenario can foreseeably result in a level 4 injury.

Steps leading to harm

Step 1: Due to the lack of instructions, the user does not use a correct AC-DC adaptor intended to properly charge the product. The product has a USB cable intended to connect to 5Vdc at a maximum current of 0.5A, a higher capacity source is used.

Step 2: The incompatible charger causes an over-voltage and/or an over-current situation which damages the BMS.

Step 3: The damaged BMS fails to adequately protect the battery resulting in an over-charge situation where the battery cell is charged to a potentially unsafe state.

Step 4: Over-charged battery cell enters thermal runaway; a sudden and aggressive fire occurs.

Step 5: A fire takes hold

Step 6: The fire results in a level 4 injury to building occupant/s.

The information indicates that in all scenarios the risks are present due to design and potential manufacturing failures. These are present on all units supplied and means that all users of the products are affected. A key variable to some of the risks is the base unit’s behaviour during wear, tear, usage, storage environment and movement, the extent of these risks is more difficult to determine on the basis of available information.

It is considered that in three of the scenarios detailed above, these are plausible at a level 2 severity of harm. In the last scenario the severity of harm is at level 4. This risk assessment takes into consideration the risk presented by more than one hazard. Where there are multiple levels of harm the overall level of risk associated with the product will usually be determined by the hazard that creates the greatest risk. However, in this circumstance there is value in taking a broader view to enable the tolerability of all risks presented by the product to be considered.

To combine hazards using the PRISM methodology, each hazard scenario needs to be comprised of the same harm level. Scenarios 1, 2 and 3 reflect scenarios relating to level 2 injury levels so can all be combined. By combining the probabilities of harm presented by the multiple harm scenarios for the different hazards could generate a greater overall probability of harm from the product.

In addition, it could also be explored whether scenario 4 which has the greatest severity of harm at level 4 should have a ‘risk level plus’ label applied.

5) Probability of harm

The following probabilities can be estimated using the available data and knowledge of human behaviour to arrive at subjective probabilities:

Scenario 1: The product can be turned on with the blades exposed

Step 1: The blender is used to make a drink directly into the detachable bottle. The user removes the bottle part which leaves the blender blades exposed.

Blenders are intended to grind semi-solid ingredients, such as fresh fruits and vegetables, into smooth purées. The inherent design of the product means the smooth purée is blended into the same bottle intended for the user to drink from, this fundamentally results in the blades becoming exposed when the user removes the detachable bottle to drink.

A probability of 1.0 is given to the likelihood that the product is used in accordance with how the product is designed and intended to be used.

Probability: 1.0

Step 2: The user does not immediately attach the blade guides for storage or transportation, these could have been lost or thrown away after purchase.

Even where there is some appreciation of the hazard, users may not recognise the risk arising from the exposed blades, and they may assume the product cannot be switched on whilst exposed. Based on best judgement, a probability of 0.1 is given.

Probability: 0.1

Step 3: The user accidently pushes the power button twice causing the blades to rotate.

The button that activates the blades sits close to the top of the base piece where the blades sit. It is foreseeable that it is easy when the bottle is removed to activate the blades. This happened accidentally at the test laboratory; therefore, a conservative ‘occasional’ qualitative value is applied.

Probability: 0.01

Step 4: The user comes into contact with the blades which cause cuts and nerve damage to the hand.

Consideration of the behaviour of the product and the behaviour of the user will be key. Predicting the behaviour of the product will be assisted by test results, and the fact the product was accidentally switched on whilst the blades were exposed within the laboratory. Predicting the behaviour of the user can be more challenging, however through careful consideration of normal and reasonably foreseeable human behaviour, taking into account the people at whom the product is aimed, the number of products available on the market, frequency of use, and through identifying key injury data and details of any specific reported injuries or ill health will assist with accessing the probability level.

In the Small Kitchen Appliances Market, the number of users within the UK is expected to amount to 19.1m users by 2029. ^{[footnote 6]} In the US, it has been reported by the Consumer Products Safety Commission (CPSC) that in one year, emergency room treated more than 7,000 injuries relating specifically to blender accidents. ^{[footnote 7]} This has seen growth within the past 10 years and is expected to increase as the number of users rise.

The probability of cuts or lacerations resulting in a level 2 injury would depend upon such factors as how quickly the user let go of the blender, the angle and severity which the blades caught the hand. The likelihood of the cuts producing a level 2 injury is estimated to be 25%.

Probability: 0.25

Compound probability = 1.0 x 0.1 x 0.01 x 0.25 = 0.00025

Scenario 2: The blades break and detach from the base

Step 1: The blender is used to make a drink directly into the detachable bottle, due to the weakness of the blade attachment the blades break and detach at the base.

As described in scenario 1, the inherent design of the product means the smooth purée is blended into the same bottle intended for the user to drink from, this fundamentally means the blades are in the detachable bottle, and if any blade parts break the only place these can go is into the bottle with the drinkable contents.

The probability here should reflect the number of incidents to date and calculate foreseeable future incidents due to the design and manufacturing failures which may affect all products during their lifespan. Incident and complaints data provided by the affected business, along with population numbers will lower the uncertainty here. Online reviews may give an indication of a poor-quality product, however the legitimacy of these need consideration before using them. Other factors may accelerate the degradation of the product, for example using hard or frozen items in some blenders with weak blades to support crushing ice would put unnecessary strain on the blades.

For illustrative purposes, a conservative occasional qualitative value of 10% of all products developing this fault is given. This would vary dependent on the results of the test reports and incident data.

Probability: 0.1

Step 2: The user removes the bottle part and does not notice that the blades are broken or missing from the base and now within the drink bottle, they drink directly from the bottle.

A level of uncertainty is here as it requires the user to not notice that the blades are missing. As the product is intended to be portable, it could be hypothesised that the user is distracted so does not notice. Potentially the product may make a noise prior to the blades breaking which would give the user some indication of an issue.

Probability: 0.01

Step 3: The blades enter the mouth through a natural drinking motion and behaviour, the user sustains cuts to their lips or mouth. ^{[footnote 8]}

It is foreseen that the user would not swallow the blades, and an injury would occur on the lips, tongue, or mouth area. Swallowing is a complicated task that needs your brain to coordinate many different muscles. When drinking, the lips create a seal for the flow into the mouth where the liquid or food is met by the tongue. The lips and jaw close to seal the mouth. The liquid is moved over the tongue and mixed with saliva, and the tongue pushes the liquid to the back of the mouth towards the pharynx. ^{[footnote 9]} The natural gag reflex is expected to expel any foreign objects rather than swallowing.

Data suggests that in relation to all reported incidents of broken blades, there is in reality a low rate of cut or laceration incidents compared to the millions of these products in use.

The likelihood of the cuts producing a level 2 injury is estimated to be 25%.

Probability: 0.25

Compound probability = 0.1 x 0.01 x 0.25 = 0.00025

Scenario 3: The PCB and motor soldering fails

Step 1: The connection of the internal PCB, motor and lithium-ion battery pack (which contains one cell) fails over time due to vibration of the motor when in use, or when the product is transported due to its portable nature.

This is difficult to determine with any certainty and is dependent on the product’s design and construction, the demographic of the user, and the number of times it is used, moved, or handled. The result of the test reports or speaking with the test house for clarity can aid the decision. For illustrative purposes it is estimated that in approximately 10% of instances the poor internal quality will result in a fault occurring during the product’s lifetime.

Probability: 0.1

Step 2: Internal parts short circuit due to parts becoming loose and touching each other, whilst the product is plugged in and in use. The product can then overheat and cause a fire hazard.

The PCB and motor are only connected by solder which is not sufficient and can fail over time with vibration and movement, this increases the likelihood of this. This is also difficult to determine with any certainty as it is dependent on a number of factors such as the loose parts touching each other whilst the product is plugged in and in use. This would be described as an unlikely event; in most circumstances the product may simply stop working.

Probability: 0.005

Step 3: A level 2 injury occurs. It if foreseen that the product is in use when the parts become loose due to the vibration, therefore quick intervention due to supervision of the product may take place.

The product overheats and heats up external surfaces. The user’s automatic reaction is to pick up the product and throw it outside, these situations happen quickly and there may be insufficient time to remove the product from the location. This results in more severe burns which cover the arms, torso and some of the face which determine approximately 20% of the total body surface.

Probability: 0.0001

Compound probability = 0.1 x 0.005 x 0.0001 = 0.00000005

Scenario 4: The user does not use the correct AC-DC adaptor to charge the product.

Step 1: Due to the lack of instructions, the user does not use a correct AC-DC adaptor intended to properly charge the product. The product has a USB cable intended to connect to a 5Vdc supply at a maximum current of 0.5A, a higher capacity source is used.

It is common for a domestic premises to contain multiple chargers, plus USB chargers in vehicles can vary in current capacity. The product does not come with a AC/DC adaptor so is reliant on the consumer providing one. A probability of 25% is given due to the lack of instructions which gives warnings and specifies the correct type.

Probability: 0.25

Step 2: The incompatible charger causes an over-voltage and/or an over-current situation which damages the BMS.

This probability is estimated as there is insufficient data available. However, the critical components in the BMS are designed with specific voltage and current ratings. Operating them above these ratings is likely to result in damage and may render the BMS unable to monitor or to intervene. It is also normal for a battery to give off some heat whilst charging, these signs could go unnoticed. This product has a single cell battery pack.

Probability: 0.0025

Step 3: The damaged BMS fails to adequately protect the battery resulting in an over-charge situation where the battery cells are charged to a potentially unsafe state.

An inadequate BMS may fail to detect and prevent an over-charge condition from occurring which may result in the battery cells exceeding their maximum safe charge voltage. This is considered very likely to occur as without BMS monitoring and intervention there are unlikely to be any additional measures in the blenders design and poor internal build quality which will prevent an over-charge condition.

Probability: 0.8

Step 4: Over-charged battery cells enter thermal runaway; a sudden and aggressive fire occurs.

This probability is estimated as there is insufficient data available. The test research carried out previously has demonstrated that overcharged battery cells do not always enter thermal runaway in all cases. It is possible that overcharged battery cells will remain in an unsafe ‘overcharged’ state without entering thermal runaway.

This is a single cell battery; therefore, a cautious probability has been selected.

Probability: 0.5

Step 5: A fire takes hold and ignites surrounding materials.

The product is portable so potentially could be in an environment which could contain the fire; however, it is reasonable to foresee a fire in a domestic setting. Data sources indicate that when a lithium-ion battery goes into thermal runaway significant fires can result in very short time frames. Additional data from the Home Office relating to fire statistics data and fire and rescue incident data ^{[footnote 10]} has been used.

Probability: 0.015

Step 6: The fire results in a level 4 injury occurs.

Probability: 0.047

Compound probability = 0.25 x 0.0025 x 0.8 x 0.5 x 0.015 x 0.047 = 0.000000176250

6) Level of risk

The steps to harm are summarised in the table below.

Scenario one: The product can be turned on with the blades exposed leading to a level 2 injury:

Steps	Probability
Step 1: The blender is used to make a drink directly into the detachable bottle. The user removes the bottle part which leaves the blender blades exposed.	1.0
Step 2: The user does not immediately attach the blade guides for storage or transportation, these could have been lost or thrown away after purchase.	0.1
Step 3: The user picks the base until up with the blades still exposed and accidently pushes the power button twice causing the blades to rotate.	0.01
Step 4: The user comes into contact with the blades which cause cuts and nerve damage to the hand. A level 2 injury occurs.	0.25

The compound probability is the sum of the probabilities at each step, which equates to 0.00025 (or 1 in 4,000).

For a level 2 injury, this is a medium-risk outcome (see PRISM guidance Table 3 in Part 1, section 2.2(vii)).

Scenario 2: The blades break and detach from the base leading to a level 2 injury:

Steps	Probability
Step 1: The blender is used to make a drink directly into the detachable bottle, due to the weakness of the blade attachment the blades break off and detach at the base.	0.1
Step 2: The user removes the bottle part and does not notice that the blades are broken or missing from the base and in the drink bottle, they drink directly from the bottle.	0.01
Step 3: The blades enter the mouth through a natural drinking motion behaviour, the user sustains substantial cuts to their lips or mouth. A level 2 injury occurs.	0.25

The compound probability is the sum of the probabilities at each step, which equates to 0.00025 (or 1 in 4,000).

For a level 2 injury, this is a medium-risk outcome (see PRISM guidance Table 3 in Part 1, section 2.2(vii)).

Scenario 3 The PCB and motor soldering fails leading to a level 2 injury:

Steps	Probability
Step 1: The connection of the internal PCB, motor and lithium-ion battery pack which contains one cell fails over time due to vibration of the motor when in use, or when the product is transported due to its portable nature.	0.1
Step 2: Internal parts short circuit due to parts becoming loose and touching each other, whilst the product is plugged in and in use. The product can then overheat and cause a fire hazard.	0.005
Step 3: It is foreseen that the product is in use when the parts become loose, therefore quick intervention due to the supervision of the product may take place. The product overheats and heats up external surfaces. The user’s automatic reaction is to pick up the product and throw it outside or away. This results in burns which cover the arms, torso and some of the face which determine approximately 20% of the total body surface (level 2 injury).	0.0001

The compound probability is the sum of the probabilities at each step, which equates to 0.00000005 (or 1 in 20,000,000).

For a level 2 injury, this is a low-risk outcome (see PRISM guidance Table 3 in Part 1, section 2.2(vii)).

Scenario 4 The user does not use the correct AC-DC adaptor to charge the product leading to a level 4 injury:

Steps	Probability
Step 1: Due to the lack of instructions, the user does not use a correct AC-DC adaptor intended to properly charge the product. The product has a USB cable intended to connect to 5Vdc at a maximum current of 0.5A, a higher capacity source is used.	0.25
Step 2: The incompatible charger causes an over-voltage and/or an over-current situation which damages the BMS.	0.0025
Step 3: The damaged BMS fails to adequately protect the battery resulting in an over-charge situation where the battery cells are charged to a potentially unsafe state.	0.8
Step 4: Over-charged battery cell enters thermal runaway; a sudden and aggressive fire occurs with energetic ‘jetting’.	0.5
Step 5: A fire takes hold.	0.015
Step 6: The fire results in a level 4 injury for occupant/s.	0.047

The compound probability is the sum of the probabilities at each step, which equates to 0.000000176250 (or 1 in 5,681,818).

For a level 4 injury, this is a low-risk outcome (see PRISM guidance Table 3 in Part 1, section 2.2(vii)).

Before combining probabilities, the highest risk outcome from all scenarios presented is medium-risk.

To determine the best approach the probabilities of those scenarios with the same injury level severity will be combined.

Scenarios 1, 2 and 3 have been identified to have independent hazards that involve the same harm level. Combining the probabilities of harm presented by the three hazards will increase the overall probability of harm, which is important in itself, and may change the overall product risk level.

Scenario 1 involves a 1 / 4,000 probability of a level 2 injury, and scenario 2 has a 1 / 4,000 probability of a level 2 injury, these have medium risk levels. Combining the probabilities produces a new probability for the product, this is calculated to be 1 in 2000. This brings the probability much closer to the boundary between medium and high risk so is significant.

First multiply the bottom numbers in a fraction, the denominators together. Then multiply the top numbers, the numerators by the opposing denominator. Then add these two numbers together.

• Example: To combine 1/4000 and 1/4000
• 4000 x 4,000 = 16,000,000
• 1 x 4,000 = 4,000
• 1 x 4000 = 4000
• 4,000 / 16,000,000 + 4000 / 16,000,000 = 8,000 / 16,000,000 = 1 in 2000

Scenario 3 has a very low overall probability of 1 / 20,000,000, so it may not add any significance if combined with the other scenario probabilities. To demonstrate, if the probability of scenario 3 is combined with probabilities of scenarios 1 and 2, the new probability is calculated to be 1 in 1,999. This increases the overall probability by a relatively small margin in terms of the change by bringing scenarios 1 and 2 together.

To include scenario 3 and calculate all 3 probabilities, combine scenarios 1 and 2 as above to generate the fraction 1 / 2000, and add this to the scenario 3 probability 1 / 20,000,000. Multiply the bottom numbers in a fraction, the denominators together 2,000 x 20,000,000 = 40,000,000,000

• Then multiply the top numbers, the numerators by the opposing denominator.
• 1 x 20,000,000 = 20,000,000
• 1 x 2,000 = 2,000
• Then add these two numbers together.
• 20,000,000 / 40,000,000,000 + 2,000 / 40,000,000,000 = 20,002,000 / 40,000,000,000 = 1 in 1,999

This product has another independent hazard that involve risks with a different injury severity level, level 4. If the risk level was also within the medium-risk category, consideration could be given to how the overall product risk is best expressed. It could be appropriate in that circumstance to apply a label of ‘medium-risk plus’, however as this scenario is a low-risk, the final risk level applied to this product is based on the combination of the two scenarios and identified as medium-risk.

7) Uncertainty

There is a medium level of uncertainty in relation to this assessment as there are gaps and/or some of the evidence used is unvalidated, old, or otherwise limited. The injury scenarios take into consideration consumer behaviour even though some behaviours can be predicted it is challenging to directly attribute human behaviour to this specific product.

Although data is available to support some of the steps there is still a level of uncertainty and judgement used. The harm scenario is largely based on predicting the behaviour of users, and the degradation of the product under numerous foreseeable situations surrounding use, storage, movement and type of use, which may or may not accelerate the incident rate, all of which come with uncertainty.

Overall, this risk assessment has a medium level of uncertainty.

Sensitivity analysis

Where there is uncertainty surrounding one or more of the probabilities within the injury scenario, then different probabilities (which can be higher, lower, or both) that fairly reflect the extent of the uncertainty have been applied. Scenarios 3 and 4 result in extremely low probabilities of harm overall, significant amendment is needed to these probabilities in order to change the risk level.

Sensitivity analysis focuses on the other scenarios. Scenarios 1 and 2 shows that the parameters need to be adjusted by more than a factor of 10 to increase the level. This determines that the outcome of the risk assessment is not particularly sensitive to changes in the probabilities, however there is value in taking a broader view of the risks presented by the product.

8) Risk evaluation

The multiple harm scenarios discussed above when evaluated together provide a more holistic view of the product’s overall risk level. The overall level of risk associated with the product will usually be determined by the hazard that creates the greatest risk. However, in this circumstance with the blender in question there are more than one hazard of concern. As such, a broader view was taken by combining hazards which placed the risk of the product much closer to the medium/high risk boundary and will be of relevant consideration in the design of corrective actions.

9) Footnotes

1. The introduction of BS EN 60335-2-14:2006+A12:2016 states: An investigation by CENELEC TC61 has shown that all risks from products within the scope of this standard are fully covered by the Low Voltage Directive, 73/23/EEC. For products having mechanical moving parts, a risk assessment in accordance with the Machinery Directive, 98/37/EC, has shown that the risks are mainly of electrical origin and consequently this directive is not applicable. However, the relevant essential safety requirements of the Machinery Directive are covered by this standard together with the principal objectives of the Low Voltage Directive. ↩

2. The Electrical Equipment (Safety) Regulations 2016 – Legislation.gov.uk ↩

3. I accidently put my finger in a hand blender accident – Mumsnet ↩

4. Example injury from hand blender – Daily Mail ↩

5. Thermal Runaway – UL Research Institutes ↩

6. Revenue in UK Small Kitchen Appliances Market – Statista ↩

7. Finger injuries from handy immersion blenders are on the rise – Consumer Reports ↩

8. PRISM level 2= cuts >10 cm on body and >5 cm on face, requiring stitches. ↩

9. The Normal Swallow – Norfolk and Norwich University Hospitals NHS Foundation Trust ↩

10. Fire Statistics – Home Office. ↩