03_hazardous_substances_and_other_chemicals_engineering_controls_and_personal_protective_equipment_20140117153253

Question 1

General ventilation or ‘dilution’ ventilation is a term used to define the flow of air into and out of a working area, so that any contaminants are diluted by adding some fresh air. It can be provided by:

Answer 1

 Natural ventilation which relies on wind pressure and temperature differences to move fresh air through a building and is usually not fully controllable.  ‘Forced’ or mechanical ventilation which uses mechanical supply and/or extraction to provide fresh air and is controllable.

Question 2

LEV might not be the right control solution when:

Answer 2

 There are a large number of widely-spaced sources  The source is large and LEV is impossible to apply over the entire source  The source position is not fixed  The source emits relatively small amounts of contaminant (which is not toxic)  The contaminant is offensive but not harmful.

Question 3

For LEV to work effectively the hood has to be carefully matched to the contaminated air source that needs to be controlled. Consideration needs to be given to the following:

Answer 3

Particle size of contaminant cloudsVisibility of particle cloudsMovement of particles in airAbrasive or corrosive particlesSticky dust, mist and condensateFlammable or combustible substances

Question 4

The basic components of an LEV system are:

Answer 4

 An inlet, for example: a hood or enclosure, to collect and contain the contaminant close to its source.  Ductwork, to convey the contaminant away from the source.  A filter / air-cleaner to remove the contaminant from the extracted air-stream (Note: the filter should normally be located before the fan).  A fan or other air-moving device to provide the necessary airflow.  Further ductwork to and outlet or exhaust which discharges the cleaned air to the outside atmosphere at a suitable point.

Question 5

Types of hood

Answer 5

Enclosing hoodsReceiving hoodsCapturing hoods

Question 6

LEV systems work effectively when the airborne contaminant cloud is contained, received or captured by the hood. The effectiveness of LEV can be judged by:

Answer 6

 How much the hood constrains the contaminant cloud.  How well the LEV induced airflow carries the contaminant cloud into the system.  How little of the contaminant cloud enters the process operator’s breathing zone.

Question 7

Types of LEV Filter / air cleaner

Answer 7

Particle collectors [Fabric filters, Cyclones, Electrostatic precipitators]Scrubbers [Venturi scrubbers, Self-induced spray collectors, Wet cyclone scrubbers, Packed tower scrubbers]

Question 8

The fan is the most common air mover. It draws air and contaminant from the hood, through ductwork to discharge. There are five general categories of fan:

Answer 8

 Propeller e.g. general or dilution ventilation  Axial not suitable for dusts  Centrifugal are the most commonly used fans for LEV systems  Turbo exhauster  Compressed-air-driven air mover.

Question 9

The following factors can reduce the effectiveness of LEV:

Answer 9

 Poor design: inappropriate inlet for type and size of contaminant cloud, or underpowered fan unable to capture contaminated air.  Poor use: system not switched on when needed, or inappropriate positioning of moveable hood.  Unauthorised modification: can imbalance a system and adversely affect air flows.  Inadequate maintenance: damaged ducting, congested filters and damaged fan blades will compromise the effectiveness of the LEV.  Changes of work activity: generating more contaminant than the LEV was designed to cope with.

Question 10

How often the LEV system should be checked depends on how complicated the system is, how likely it is to fail, and the consequences if it does. Regular maintenance inspections should be made of the following areas:

Answer 10

 moving parts that may wear, such as fan bearings or filter shakers  non-moving parts, such as hoods, ductwork and seals (which can suffer physical or chemical damage and wear)  parts that deteriorate with use, such as filters or flexible ducting  items that need regular attention, such as filters that need replacing, or removing sludge from a wet scrubber. This may involve daily operator checks and periodic checks by managers.

Question 11

A variety of qualitative and quantitative methods can be used to assess the performance of LEV. Qualitative assessment techniques

Answer 11

The ‘dust lamp’ or ‘Tyndall illumination’ makes fine particles visible. The ‘Tyndall effect’ is the forward scattering of light. This is commonly seen when a shaft of sunlight entering a building shines through mist, dust or fume in the air. The ‘dust lamp’ reproduces this effect by producing a powerful parallel beam of light (see Figure 3.7). It shows the density and movement of particle clouds in its path. The lamp should be moved to illuminate different parts of the cloud and indicate the full cloud size and behaviour.Other forms of observational assessment can be made using smoke from pellets, smoke tubes or smoke generators. These can:  show the size, velocity and behaviour of airborne contaminant clouds  identify capture zones and boundaries  confirm containment within a hood  identify draughts, their direction and size  show the general movement of air.

Question 12

A variety of qualitative and quantitative methods can be used to assess the performance of LEV. Quantitative assessment techniques

Answer 12

Inlet Face or capture velocity. See Figure 3.10. Ducts Transport (duct) velocity is measured in a straight section of duct, well downstream of bends and other turbulence sources. The duct velocity must be sufficient to keep the particles airborne (otherwise) particles may settle out in the ductwork and affect the overall efficiency of the system. The actual dust velocity required is determined by considering the nature of the particles that the system is handling such as size and density. An anemometer e.g. thermal anenometer or hot wire, velometer 
or a pitot-static tube could be used. The choice of instrumentation is governed by the air velocity in the duct (a thermal anemometer is more suitable if this is less than 3ms-1). An anemometer responds to the cooling effect of airflow and the pitot-static tube measuring, via a pressure gauge, velocity pressure which can then be converted to velocity. Fan/air mover Measures can be taken of: fan direction and speed; the pressure difference across the fan; and the volume flow rate. A big difference in pressure across the fan (i.e. resistance) indicates that the system will not be as efficient. Air cleaner Filters: pressure differential across the filter. Wet scrubber: pressure difference at the inlet and outlet, and the water pH if relevant to the scrubbing performance. Air sampling Additionally, air sampling may be carried out as proof of the efficiency of a LEV system and effective control of the contaminant where the hazard and potential risk is great. (See element B4). Air sampling may also include testing emission levels from the exhaust e.g. volatile organic compounds (VOCs). When carrying out testing all instruments should be calibrated; and where there may be flammable atmospheres intrinsically safe instruments should be used.

Question 13

A thorough examination and testing of LEV can be considered to comprise three stages:

Answer 13

Stage 1: a thorough visual examination to verify the LEV is in efficient working order, in good repair and in a clean condition. Stage 2: measure and examine the technical performance to check conformity with commissioning or other sources of relevant information. Stage 3: assess whether the control of worker exposure is adequate.

Question 14

PPE should be regarded as the last resort to protect against risks to health and safety. Engineering controls and safe systems of work should be considered first. This is because:

Answer 14

 PPE protects only the person wearing it, whereas measures controlling the risk at source can protect everyone at the workplace.  Maximum levels of protection are seldom achieved with PPE in practice and the actual level of protection is difficult to assess.  If RPE is used incorrectly, or is badly maintained, the wearer is unlikely to receive adequate protection.  RPE is uncomfortable to wear and is an intrusion into normal activities.  RPE may interfere with work.

Question 15

Type and level of protection required The risk assessment will indicate the type of protection required from:

Answer 15

 type of substance and its nature e.g. corrosive, toxic etc.  form of the substance  route of entry into the body  concentration of the substance.

Question 16

There are two broad categories of RPE:

Answer 16

respirators and breathing apparatus (BA)

Question 17

The key factors in selecting appropriate RPE are:

Answer 17

 The level of oxygen present in the air to be breathed  The presence of toxic chemicals that may pose an imminent risk to life.

Question 18

Respirators work by

Answer 18

filtering contaminants out of the air so that the wearer breathes clean air

Question 19

BA works by

Answer 19

delivering a supply of breathable air from an uncontaminated source

Question 20

Types of Respirators

Answer 20

SimplefilteringrespiratorsPowerassistedrespirators

Question 21

Types of Breathing Apparatus

Answer 21

Fresh air hoseBAPowered airlineBASelf-contained BA

Question 22

There are three main types of respirator filters:

Answer 22

Particle filters Gas/vapour filters Combined filters

Question 23

Filter efficiency

Answer 23

P1: low efficiency: used with PF4 respirators. Do not use against fume unless 
the manufacturer can guarantee protection. P2: medium efficiency: used with PF10 respirators. Not to be used against fume unless the manufacturer can guarantee protection. P3: high efficiency: used with PF20 or PF40 respirators.

Question 24

Gas and vapour filters The classification of gas and vapour filters is based on how much of the specified contaminant they can hold in a laboratory test at set conditions.

Answer 24

 Class 1: low capacity.  Class 2: medium capacity.  Class 3: high capacity.

Question 25

RPE should only be selected and used after a justification has been made in the risk assessment required by law. It can be used in the following situations:

Answer 25

 Where an inhalation exposure risk remains after other reasonable controls have been put in place i.e. residual risk.  Short-term or infrequent exposures where other controls at source are not reasonably practicable.  While putting in place other control measures (interim measures).  Emergency escape for safe exit from an area where hazardous substances may be released suddenly in the event of control systems failures e.g. a chlorine tank.  Emergency work or temporary failure of controls where other means of controls 
are not reasonably practicable.  Where emergency rescue by trained personnel is necessary.

Question 26

Selection of RPE In order to decide on the suitability and selection the following factors must be taken into account:

Answer 26

1) Chemical and toxicological related factors 2) Task-related factors 3) Worker related factors.

Question 27

A confined space is

Answer 27

a substantially enclosed space e.g. a chamber, tank, vat, silo, pit, trench, pipe, sewer, flue, well or small room with limited access and inadequate air exchange. A confined space may not necessarily be enclosed on all sides.

Question 28

Task-related factors that need to be considered when selecting RPE:

Answer 28

Work rate Wear time Abnormal temperature or humidity Power tools used Clarity of vision Clarity of communication Mobility Congested work area Potentially explosive atmosphere

Question 29

Assigned protection factor (APF) The APF is the level of respiratory protection that can realistically be expected to be achieved in the workplace by 95% of adequately trained and supervised wearers using a properly functioning and correctly fitted respiratory protective device. It is calculated, under test conditions by

Answer 29

dividing the level of air borne contamination by the level that would be breathed in (i.e. after the RPE has done its job). If there were 50mg/m3 of contaminant in the air and 5mg/m3 got passed the RPE the APF would be 50/5 = 10.

Question 30

The minimum protection required (MPR) from specific RPE can be calculated by

Answer 30

measuring the workplace concentration outside the facepiece of the RPE and dividing it by the maximum allowable concentration inside the facepiece of the RPE (i.e. the WEL) MPR = workplace concentration of contaminant outside RPE facepiece maximum allowable concentration inside the RPE facepiece (WEL)

Question 31

It should be noted that RPE may not provide the level of protection stated by the manufacturers. This may be because:

Answer 31

 Poor air flow or a reduction in battery power  The fitting of incorrect cartridges or a failure to replace them before saturation  Equipment incorrectly fitted or incompatible with other personal protective equipment being worn  The presence of other contaminants resulting in a decrease in saturation time  Inadequate training in its use and particularly in the care that should be taken in its removal  Poor maintenance and inadequate storage resulting in the face piece being left exposed  Damage occurring during use and inadequate monitoring and supervision to ensure the equipment was always used when required  The equipment might not have been manufactured to the appropriate standards.

Question 32

There are two basic types of RPE fit testing

Answer 32

Qualitative fit testing: is a simple pass/fail test based on the wearer’s subjective assessment of the leakage, via the face seal region, of a test agent. If the wearer can detect the test agent (either a bitter or sweet tasting aerosol; or an odourous compound) the fit test is failed. Quantitative fit testing: provides a numerical measure of the fit that is called a fit factor. These tests give an objective measure of face fit. They require specialised equipment and are more complicated to carry out.

Question 33

Maintenance is a requirement for all RPE, except for single use RPE, and should be carried out by properly trained personnel. An effective maintenance system includes the following:

Answer 33

 Examination: checking for faults, damage, wear and tear, dirt etc.  Testing: to ensure PPE is operating as intended  Cleaning: including disinfection if appropriate  Repair  Replacement. Records of examination and testing must be kept for five years.

Question 34

When choosing safety eye wear the following should be considered:

Answer 34

The nature of the hazardThe risk factorsIntended useType of lensOcular performanceComfort and fitCompatibility with other PPE

Question 35

After considering the specific requirements of skin and eye protection, the following general issues should be considered:

Answer 35

 Consultation and user trials  Comfort of the equipment  That everything purchased carried the CE mark  That all personal protective equipment provided met the appropriate standards.

Question 36

The following training should be given to users of PPE:

Answer 36

 The health risks of the chemical in use.  The type of personal protection to be used and the reason for its use.  The methods to be used for putting on and taking off the equipment without causing contamination including decontaminating or discarding gloves after use.  The methods of examining the equipment for damage or degradation, particularly gloves, and for reporting defects and obtaining replacements.  How to store the equipment correctly.  How to carry out self-examination of the skin and the action to be taken if problems were to occur.

Question 37

Other than training, there are practical measures that can be taken to increase the correct use of PPE. These include:

Answer 37

 Management leading by example  Employees being involved in the selection of the equipment  Ensuring the availability of a range of sizes in gloves and fully adjustable face shields  Ensuring employees were required to sign for their equipment and maintaining records of issue  Issuing the equipment on a personal basis and providing adequate storage facilities  Using propaganda, signs and posters and incentive schemes  Monitoring compliance in the use of the equipment with a recognised code of discipline for non-use  Monitoring the effectiveness of the equipment issued and replacing it with an alternative type if problems were encountered.

Question 38

A welder undertakes work in an open plan workshop. Outline the factors to be considered when selecting suitable Respiratory Protective Equipment for this work. 10 marks

Answer 38

Factors relating to the individual, task and substance that should be considered include:  the type, duration and frequency of the work and its position in the workplace  the fume control measures currently in place such as general or local exhaust ventilation  the health hazard category of the welding fume for example whether toxic or irritant  the level of protection (protection factor) required for each substance based on considerations such as the amount of the substance, the volatility of the welding consumables, the concentration and particle size and the relevant workplace exposure limits (WELs)  the choice of the equipment in relation to the protection factor whether half face, full face or forced air breathing apparatus  the choice of the correct filter type based on the determined protection factor  task related factors such as the work rate and wear time, the presence of humidity, the need for mobility and communication and the amount of physical effort and degree of movement required to carry out the task  the fit and comfort of the equipment taking into account facial hair and the need to wear spectacles  the compatibility of the equipment with other personal protective equipment such as eye, head or hearing protection  the heat resistant properties of the equipment  the battery life of specified types of equipment  the cost of the equipment and the amount of training and maintenance required for its use  the manufacture of the equipment to recognised standards  any relevant medical conditions of the potential user such as heart disease, asthma or claustrophobia.

Question 39

You have been sent a copy of a ‘local exhaust ventilation (LEV) examination and test report’ conducted by an external organisation. The report relates to an LEV system in one part of your company’s production area. The production manager has asked you to comment on the suitability of this report before the company commissions further LEV examination and testing work throughout the rest of the factory. (a) Outline the measurements that you would expect to have been taken as part of the examination and test of the LEV system. 4 marks (b) In addition to these measurements outline other information that should be contained in the report. 16 marks

Answer 39

Measurements that should have been taken in examining and testing the LEV system should have included:  the face velocity across the hood or opening  the capture velocity; the duct velocity  the pressure drop across the filter or fan  the static pressure in the hood or duct and the fan/motor speed  the power consumption The report should additionally contain information such as:  The name and signature of the person carrying out the examination together with evidence of their competence.  The date the examination was carried out together with the date of the previous examination and test so that an assessment can be made as to whether the interval between them was appropriate in accordance with the requirements of the COSHH Regulations.  The location and extent of the LEV system being examined.  The process and hazardous substance it is intended to control. A diagram of the layout of the system with the test points marked should be attached as should also information on the system’s designed performance, its commissioned performance and that noted at the last test. As for the current test and examination, the report should:  note the conditions which appertained at the time, either normal or special  state the methodologies and equipment used to measure the performance of the system such as, for example, anemometers, manometers or pitot tubes. This will enable a decision to be made as to whether the methodologies used are in line with those set out in the relevant HSE Guidance. Other matters which should be addressed in the report include:  the calibration of the measuring equipment  a record of the actual measurements and observations made  results of any air sampling relevant to the performance of the LEV system or emissions to atmosphere  details of adjustments or minor repairs made to improve the effectiveness of the system and any remaining repairs or alterations that are required to restore its performance and whether advice has been given to the recipient of the report that the record should be maintained for a period of five years.

Question 40

An airborne contaminant has a Workplace Exposure Limit (WEL) of 10ppm, 8-hour time- weighted average (TWA). Engineering controls have been introduced but the airborne concentration of the contaminant in a workshop has been measured at 180ppm, 8-hour TWA. The occupational hygienist has selected a piece of respiratory protective equipment (RPE) with an assigned protection factor (APF) of 20, which is to be worn temporarily by all employees in the contaminated area. (a) Using the data above outline how the hygienist could have calculated the APF AND outline whether the hygienist has made an appropriate selection. 4 marks

Answer 40

 The concentration of contaminant in the air is 180ppm.  The WEL of 10ppm gives us the maximum concentration in the face piece that the employee should be exposed to. So, the minimum protection required (MPR) can be calculated as 180 \ 10 = 18which means the minimum APF of the RPE for this situation is 18 The chosen piece of equipment has an APF of 20, which would, in-fact, lead to an exposure within the face piece of 180 \ 20 = 9 ppm … lower than the WEL of 10ppm. The chosen piece of equipment is therefore appropriate for use. Note: A higher factor of safety could of course have been obtained by selecting respiratory protective equipment with an even higher APF.

Question 41

A large manufacturer uses hydrochloric acid in a large open tank to remove rust from sheet steel. This creates acid mist in the immediate work area and the company has decided to install a local exhaust ventilation (LEV) system. This system consists of an inlet, ducting, air cleaner, air mover and exhaust. (a) For EACH of the components listed above outline the design features required for the LEV system to be effective. 10 marks

Answer 41

The hood would need to be of a suitable size to cover the tank and have a face velocity adequate to capture the acid mist. The ducting, because of the acidic nature of the contaminant, would have to be corrosion resistant, be smooth with rounded bends, of size appropriate for the required transport velocity and provided with access for testing and maintenance. The air cleaner would probably be by means of a wet scrubber, possibly in combination with an alkali neutraliser, with appropriate means for disposing of effluent. The fan, either axial or centrifugal, would need to be corrosion resistant, of sufficient power to provide the necessary extraction velocity and be designed to minimise noise generation. The exhaust outlet should be located following consideration of all environmental implications including noise, should be corrosion resistant and should be fitted with a weather cowl and deflector baffles to prevent the entry of vermin.

Question 42

(b) Explain the requirements of the Control of Substances Hazardous to Health (COSHH) Regulations 2002 for inspection and testing of the LEV system. 3 marks

Answer 42

A periodic visual inspection of a local exhaust ventilation system together with a thorough examination and test must be carried out by a competent person at least once in every period of fourteen months. A record of the examinations must be kept available for at least five years from the date on which they were carried out.

Question 43

(c) The LEV system breaks down and will take a number of weeks to repair. In the meantime the employees will need to use respiratory protective equipment (RPE) to control their exposure to the acid mist. Outline factors to be considered when selecting the RPE to protect the employees whilst engineers are repairing the LEV system. 7 marks

Answer 43

Factors to be considered in the selection of the equipment would be:  its type either full face or half mask  the protection factor required  the selection of the correct cartridges with respect to the acid mist and the battery life of the chosen equipment. Task related factors would also be important such as:  the degree of movement required by the wearer  their work rate  the compatibility of the respirators with other personal protective equipment such as eye protection  the comfort factor. Cost factors would also have to be considered such as those involved in the maintenance and storage of the equipment and that which would be necessary to provide training for the user in fit testing for close fitting respirators.

Question 44

A grounds maintenance contractor is selecting eye protection to wear during grass strimming. (a) Describe the specific features of the eye protection required for this task. 7 marks (b) Outline the arrangements the grounds maintenance contractor should put in place when the selected eye protection is in use. 3 marks

Answer 44

In carrying out the task described, the probability would be that impact might come from a variety of directions and as a consequence goggles or a face shield should be selected as eye protection. They would need to:  have good mechanical and impact strength  be shatterproof with medium energy impact  be adjustable to allow appropriate fit and comfort  be compatible with other personal protective equipment such as hearing, head or respiratory protection. Other possible features to be considered would be:  the optical class of the lenses  their resistance to misting and surface damage  the resistance of the frames to dusts. Finally the protection should be CE marked and comply with a recognised standard. Arrangements should be made for:  the provision of training in its use and its correct fitting with other equipment  the cleaning and storage of the equipment  reporting defects and providing replacements when these are seen to be necessary. Additionally, measures should be taken to ensure that the protection is used at all times when grass strimming is being carried out with disciplinary action being taken for non-use.

Question 45

A local exhaust ventilation (LEV) system is used to reduce exposure of workers to dust in the workplace. (a) Identify THREE visual inspection methods that could be used to give a simple qualitative assessment of the effectiveness of the LEV system. 3 marks

Answer 45

Suitable methods included:  the use of equipment such as a Tyndall beam (dust lamp)  the use of smoke from pellets, tubes or generators  observations on the build of dust on surfaces in the workplace.

Question 46

(b) Transport velocity is one of the quantitative measurements undertaken to assess the performance of the LEV system. (i) Outline why transport velocity is an important parameter to measure when assessing the effectiveness of the LEV system. 2 marks

Answer 46

(i) Transport velocity is an important parameter because an insufficient transport velocity can result in dust particles settling in the duct and lead to a blockage of the duct. As well as reducing the overall efficiency of the LEV system, there is an increased fire or explosion risk.

Question 47

(ii) Outline the methods that can be used to measure transport velocity in a LEV system. 5 marks

Answer 47

(ii) Methods that could be used to measure transport velocity include: A thermal or hot-wire anemometer, which consists of an electrically heated wire exposed to the air stream (carrying the particles) through the duct. The speed of the air stream affects the rate at which the wire loses heat. Typically, the speed/velocity is determined by measuring the electrical current necessary to maintain the wire at a constant temperature. A pitot-static tube (attached to a pressure gauge) detects airspeed by placing a hollow tube into the air stream. As air jams into the end of the tube, it creates pressure. By comparing the pressure inside the tube with the natural pressure of the air around the tube (the static pressure), you get an accurate measure of airspeed.

Question 48

(b) Outline other factors that should be taken into account when selecting appropriate RPE. 6 marks

Answer 48

Other factors include:  the nature of the dust or vapour involved  comfort factors such as the length of time that employees would need to wear the equipment and the type of work to be carried out, taking into account its physical nature, the degree of movement required and the restrictions of the working space  whether fit testing would be required, the ease with which the equipment can be put on and the amount of training required  the manufacture of the equipment to an appropriate standard and its cost and durability  the ease of maintenance for example for cleaning and changing filters  its compatibility with other forms of personal protective equipment  the need to consult fully with the workforce on the selection of the equipment.