Division 6.3 Sensitivity analysis
United Kingdom
The factors used to calculate the risk of an injury scenario, namely the severity of the injury and the probability, often have to be estimated. This creates uncertainty. Probability in particular can be difficult to estimate, since the behaviour of consumers, for example, can be difficult to predict. Does a person perform a certain action often or only occasionally?
It is therefore important to consider the level of uncertainty of the two factors and to make a sensitivity analysis. The purpose of this analysis is to establish how much the risk level varies when the estimated factors vary. The example provided on the table below only shows the variation of probability, since the severity of the injury is usually predicted with more certainty.
A practical way of performing the sensitivity analysis is to repeat the risk assessment for a certain scenario, but to use a different probability for one or more steps in the scenario. For example, a candle containing seeds could cause a fire, because the seeds can catch fire and generate high flames. Furniture or curtains can catch fire and persons not in the room could inhale toxic fumes and suffer fatal poisoning:
| Injury scenario | Injury type and location | Severity of injury | Probability of injury | Resulting probability | Risk |
|---|---|---|---|---|---|
| Seeds or beans catch fire generating high flames. Furniture or curtains catch fire. Persons are not in room, but inhale toxic fumes. | Fatal poisoning | 4 |
| 0 00675 > 1/1 000 | Serious |
The probability levels for the steps in the scenario were estimated as shown in the table.
The overall probability is 0,00675, which corresponds to > 1/1 000 in table 4. This leads to the conclusion of ‘serious risk’. Note that the exact probability is closer to 1/100 than to 1/1 000, which already gives some confidence in the risk level because it is a little deeper in the serious risk area of table 4 than the > 1/1 000 row suggests.
Suppose we are uncertain about the 5 % probability that persons inhale the toxic fumes. We could put it at a much lower 0,1 % (0 001 = 1 in a thousand). If we recalculate with that assumption, the overall probability is 0,000135, which translates into > 1/10 000. Nevertheless, the risk is still serious. Even if for some reason the probability were to be a factor of 10 lower, the risk would still be high. Therefore, although the probability may vary 10- or 100-fold, we still find a serious or high risk (the latter being quite close to ‘serious’). Thus, this sensitivity analysis lets us confidently assess the risk as serious.
In general, however, risk assessment should be based on ‘reasonable worst cases’: not too pessimistic on every factor, but certainly not too optimistic.
Table 1
Consumers
| Consumers | Description |
|---|---|
| Very vulnerable consumers | Very young children: 0 to 36 months Others: Persons with extensive and complex disabilities |
| Vulnerable consumers | Young children: Children older than 36 months and younger than 8 years. Older children: Children 8 to 14 years Others: Persons with reduced physical, sensory or mental capabilities (e.g. partially disabled, elderly, including those over 65, with some reduction in their physical and mental capabilities), or lack of experience and knowledge |
| Other consumers | Consumers other than very vulnerable or vulnerable consumers |
Table 2
Hazards, typical injury scenarios and typical injuries
| NB: This table is for guidance only; the typical injury scenarios should be adapted when preparing a risk assessment. There is specific risk assessment guidance for chemicals, cosmetics and possibly others. It is highly recommended to use this specific guidance when assessing such products. See section 3.2. | |||
| Hazard group | Hazard(product property) | Typical injury scenario | Typical injury |
|---|---|---|---|
| Size, shape and surface | Product is obstacle | Person trips over product and falls; or person bumps into product | Bruising; fracture, concussion |
| Product is impermeable to air | Product covers mouth and/or nose of a person (typically a child), or covers internal airway | Suffocation | |
| Product is or contains small part | Person (child) swallows small part; the part gets stuck in larynx and blocks airways | Choking, internal airway obstruction | |
| Possible to bite off small part from product | Person (child) swallows small part; the part gets stuck in the digestive tract | Digestive tract obstruction | |
| Sharp corner or point | Person bumps into sharp corner or is hit by moving sharp object; this causes a puncture or penetration injury | Puncture; blinding, foreign body in eye; hearing, foreign body in ear | |
| Sharp edge | Person touches sharp edge; this lacerates the skin or cuts through tissues | Laceration, cut; amputation | |
| Slippery surface | Person walks on surface, slips and falls | Bruising; fracture, concussion | |
| Rough surface | Person slides along rough surface; this causes friction and/or abrasion | Abrasion | |
| Gap or opening between parts | Person puts a limb or body in opening and finger, arm, neck, head, body or clothing is trapped; injury occurs due to gravity or movement | Crushing, fracture, amputation, strangulation | |
| Potential energy | Low mechanical stability | Product tips; person on top of product falls from height, or person near product is hit by the product; electrical product tips, breaks and gives access to live parts, or continues to work heating nearby surfaces | Bruising; dislocation; sprain; fracture, concussion; crushing; electric shock; burns |
| Low mechanical strength | Product collapses by overloading; person on top of product falls from height, or person near product is hit by the product; electrical product tips, breaks and gives access to live parts, or continues to work heating nearby surfaces | Bruising; dislocation; fracture, concussion; crushing; electric shock; burns | |
| High position of user | Person at high position on the product loses balance, has no support to hold on to and falls from height | Bruising; dislocation; fracture, concussion; crushing | |
| Elastic element or spring | Elastic element or spring under tension is suddenly released; person in the line of movement is hit by the product | Bruising; dislocation; fracture, concussion; crushing | |
| Pressurised liquid or gas, or vacuum | Liquid or gas under pressure is suddenly released; person in the vicinity is hit; or implosion of the product produces flying objects | Dislocation; fracture, concussion; crushing; cuts (see also under fire and explosion) | |
| Kinetic Energy | Moving product | Person in the line of movement of the product is hit by the product or run over | Bruising; sprain; fracture, concussion; crushing |
| Parts moving against one another | Person puts a body part between the moving parts while they move together; the body part gets trapped and put under pressure (crushed) | Bruising; dislocation; fracture; crushing | |
| Parts moving past one another | Person puts a body part between the moving parts while they move close by (scissor movement); the body part gets trapped between the moving parts and put under pressure (shearing) | Laceration, cut; amputation | |
| Rotating parts | A body part, hair or clothing of a person is entangled by the rotating part; this causes a pulling force | Bruising; fracture; laceration (skin of the head); strangulation | |
| Rotating parts close to one another | A body part, hair or clothing of a person is drawn in by the rotating parts; this causes a pulling force and pressure on the body part | Crushing, fracture, amputation, strangulation | |
| Acceleration | Person on the accelerating product loses balance, has no support to hold on to and falls with some speed | Dislocation; fracture, concussion; crushing | |
| Flying objects | Person is hit by the flying object and depending on the energy sustains injuries | Bruising; dislocation; fracture, concussion; crushing | |
| Vibration | Person holding the product loses balance and falls; or prolonged contact with vibrating product causes neurological disorders, osteoarticular disorder, trauma of the spine, vascular disorder | Bruising; dislocation; fracture; crushing | |
| Noise | Person is exposed to noise from the product. Tinnitus and hearing loss may occur depending on sound level and distance | Hearing injury | |
| Electrical Energy | High/low voltage | Person touches part of the product that is at high voltage; the person receives an electric shock and may be electrocuted | Electric shock |
| Heat production | Product becomes hot; a person touching it may sustain burns; or the product may emit molten particles, steam, etc., that hits a person | Burn, scald | |
| Live parts too close | Electric arc or sparks occur between the live parts. This may cause a fire and intense radiation | Eye injury; burn, scald | |
| Extreme temperatures | Open flames | A person near the flames may sustain burns, possibly after clothing catches fire | Burn, scald |
| Hot surfaces | Person does not recognise the hot surface and touches it; the person sustains burns | Burn | |
| Hot liquids | Person handling a container of liquid spills some of it; the liquid falls on the skin and causes scalds | Scald | |
| Hot gases | Person breathes in the hot gases emitted from a product; this causes lung burn; or prolonged exposure to hot air causes dehydration | Burn | |
| Cold surfaces | Person does not recognise the cold surface and touches it; the person sustains frostbite | Burn | |
| Radiation | Ultraviolet radiation, laser | Skin or eyes of a person are exposed to radiation emitted by the product | Burn, scald; neurological disorders; eye injury; skin cancer, mutation |
| High intensity electromagnetic field (EMF) source; low frequency or high frequency (microwave) | Person is close to the electromagnetic field (EMF) source, body (central nervous system) is exposed | Neurological (brain) damage, leukaemia (children) | |
| Fire and explosion | Flammable sub stances | Person is near the flammable substance; an ignition source sets the substance on fire; this causes injuries to the person | Burn |
| Explosive mixtures | Person is near the explosive mixture; an ignition source causes an explosion; the person is hit by the shock wave, burning material and/or flames | Burn, scald; eye injury, foreign body in eye; hearing injury, foreign body in ear | |
| Ignition sources | The ignition source causes a fire; a person is injured by flames, or intoxicated by gases from the house fire | Burn; poisoning | |
| Overheating | Product overheats; fire, explosion | Burn, scald; eye injury, foreign body in eye; hearing injury, foreign body in ear | |
| Toxicity | Toxic solid or fluid | Person ingests substance from product, e.g. by putting it in mouth, and/or substance gets on skin | Acute poisoning; irritation, dermatitis |
| Person breathes in solid or fluid, for example vomited material (pulmonary aspiration) | Acute poisoning in lungs (aspiration pneumonia); infection | ||
| Toxic gas, vapour or dust | Person inhales substance from product; and/or substance gets on skin | Acute poisoning in lungs; irritation, dermatitis | |
| Sensitising substance | Person ingests substance from product, e.g. by putting it in mouth; and/or substance gets on skin; and/or person inhales gas, vapour or dust | Sensitisation; allergic reaction | |
| Irritating or corrosive solid or fluid | Person ingests substance from product, e.g. by putting it in mouth, and/or substance gets on skin or in eyes | Irritation, dermatitis; skin burn; eye injury, foreign body in eye | |
| Irritating or corrosive gas or vapour | Person inhales substance from product, and/or substance gets on skin or in eyes | Irritation, dermatitis; skin burn; acute poisoning or corrosive effect in lungs or in eyes | |
| CMR substance | Person ingests substance from product, e.g. by putting it in mouth, and/or substance gets onto skin; and/or person inhales substance as gas, vapour or dust | Cancer, mutation, reproductive toxicity | |
| Microbiological contamination | Microbiological contamination | Person gets into contact with contaminated product by ingestion, inhalation or skin contact | Infection, local or systemic |
| Product operating hazards | Unhealthy posture | Design causes unhealthy posture of person when operating the product | Strain; musculoskeletal disorder |
| Overexertion | Design requires use of considerable force when operating the product | Sprain or strain; musculoskeletal disorder | |
| Anatomical unsuitability | Design is not adapted to human anatomy, which makes it difficult or impossible to operate | Sprain or strain | |
| Ignoring personal protection | Design makes it difficult for a person wearing protection to handle or operate the product | Various injuries | |
| Inadvertent (de)activation | Person can easily (de)activate product, which leads to unwanted operation | Various injuries | |
| Operational inadequacy | Design provokes faulty operation by a person; or product with a protective function does not provide expected protection | Various injuries | |
| Failure to stop | Person wants to stop the product, but it continues to operate in situation where this is unwanted | Various injuries | |
| Unexpected start | Product shuts down during a power failure, but resumes operation in a hazardous way | Various injuries | |
| Inability to stop | In an emergency situation, person is not able to stop operation of the product | Various injuries | |
| Inadequately fitting parts | Person tries to fit a part, needs too much force to fit, product breaks; or part is too loosely fitted and becomes loose during use | Sprain or strain; laceration, cut; bruising; entrapment | |
| Missing or incorrectly fitted protection | Hazardous parts are reachable for a per son | Various injuries | |
| Insufficient warning instructions, signs and symbols | User does not notice warning instructions signs and/or does not understand symbols | Various injuries | |
| Insufficient warning signals | User does not see or hear warning signal (optical or audio), causing dangerous operation | Various injuries | |
Table 4
Risk level from the combination of the severity of injury and probability
| Probability of damage during foreseeable lifetime of the product | Severity of injury | ||||
|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | ||
| High  Low | >50 % | H | S | S | S |
| > 1/10 | M | S | S | S | |
| > 1/100 | M | S | S | S | |
| > 1/1 000 | L | H | S | S | |
| > 1/10 000 | L | M | H | S | |
| > 1/100 000 | L | L | M | H | |
| > 1/1 000 000 | L | L | L | M | |
| < 1/1 000 000 | L | L | L | L | |
Notes on Division
Footnotes
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If you need more information on the Risk Assessment method for harmonised products (both consumer and professional products) in relation to broader categories of public risks protected under EU harmonisation legislation, please refer to Part I, Chapter 5.3.