1) A) ignition sources to the primary dust explosion 6 marks
Fragment of metal inside the fine mesh filter
Rattling noise inside the pipework
From the vessel inside the bakery, the flour is pneumatically conveyed at high speed inside narrow
steel pipework that runs horizontally and vertically along pipe racks, to the respective bread-mixing
machines. – HSG 103 (66)
Humidity – L138
Ingredients are mixed at 360 RPM for 4 minutes to produce a dough.
Proofing (chemical reaction)
Oven (HEAT) – L138 (94)
Door open for fresh air (OXYGEN) – HSG L138 (110)
Speciality flour is manually emptied from these sacks into mixing machines, with the empty
sacks being flattened or folded ready for disposal. HSG 103 (48)
Old LEV = need servicing (flour leaking from the LEV), excees flour on the floor (sweeping
alot) (L138 – 216) really good
L138 (113) – maintenance activities risk of error
1) B) Primary explosion – 10 MARKS
Leaking lev – OXYGEN 216
Narrow walkways – CONFINEMENT
1) C) Secondary explosion
Leaking LEV
Air currents carry dust particles in area
Visual checks
Low ceiling
1) D) control measures to minimise secondary explosion 12 MARKS – HSG 103 Plant
design and controls (mitigation measures)
Should dust explosions occur, they are mitigated by: Mitigation measures
Ensuring a high level of housekeeping to remove dust deposits outside of handling equipment,
so that dust is not available to cause secondary explosions.
Making use of isolation mechanisms to isolate explosions inside one item of plant so that
combusting dust and gas cannot escape to other parts of the equipment.
Using explosion suppression to detect and immediately suppress dust explosions inside
handling equipment so the explosion does not have time to fully develop.
Fitting explosion relief mechanisms, such as explosion relief vents, panels and bursting discs,
so that combusting expanding dust and gases are able to escape safely to the atmosphere in a
controlled manner.
2) Why forklifts are unstable 12 MARKS
24 hours a day throughout the year
Many (100) workers = BUSY
Overhead piping, beams, and fluorescent lighting run across the bakery’s low ceilings
The buildings are at the centre of a network of service roads crossing the site
Damaged racking
Excess flour on the floor - HSG 136 (39)
Operate in all weather conditions
Potholes – HSG 136 (39)
Racing track
Discarded loads and broken pallets along the FLT vehicle routes. Workers regularly have to clear
loaves of bread from these routes. HSG 136 (39)
Drivers sometimes travel sideways across a slope if it will save them time. INDG457
The treads of the pneumatic tyres are worn smooth and the speed at which the drivers corner around
sharp bends (sometimes with elevated loads) often causes the FLTs to lose control.
3) A) 8 MARKS
Quiet shift
Supervised by two experienced workers
Routine maintenance activity = not complex
The conveyor had been electrically isolated using a Lock Out Tag Out system
Allowed to cool for almost 2 hours
Barriers were erected around the machinery
Signage to warn of the maintenance activity
Electric motor was removed, the trainees decided that it needed replacing due it its condition and age
The correct model was collected from the spare’s storage room
The trainees used the equipment manufacturer’s manual as a guide
Some of the guards around the machinery’s gears and chains were removed to provide better access.
3) B) 10 MARKS
24-hour operation
Unsupervised
No PTW or SSofW
The trainees did not do this type of work before
RUSH
Machinery guards not put back
Electrical faults
3) C) NOT FINISHED
Based on the scenario, there are various parts of the bakery that are need of maintenance. Primarily,
the dust extractors.
The frequency of the maintenance programme will depend on how important the machinery is in the
bakery’s operation. It will depend on the machinery’s role and whether it will affect other machinery on
the same production line. This is to productively minimise the lost time for maintenance work and
ensure the machinery is back in safe and proper operation. Another factor to consider, is how complex
the machinery is when deciding maintenance work. Obviously, any piece of machinery will have
several components. Some of which are easily accessible and some require a total strip down
process. The strip-down will undeniably delay operation causing down time. Repair of such
components of complex machinery needs to be considered.
4) A) Pre-demolition survey
Planning
The client must provide pre-construction information to designers and contractors
Substances may cause hazards
It is important to determine the structural condition, as deterioration may impose restrictions on the
demolition method. There may be seriously weakened structural members or connections due to
corrosive atmospheres (humidity), arising from the process used on the premises, or the structure may
be dilapidated through exposure to the elements or vandalism
Maintaining a safe means of access and egress for workers - by maintaining housekeeping at a high
standard
PTW
The need to isolate the demolition area so that potential hazards may be confined. This precaution will
also help to exclude from the site persons not directly involved in the work.
4) B)
5) A) positive aspects of traffic management (5 MARKS) inside the storage and distribution
warehouse
Each FLT is fitted with an automatic, audible reversing alarm.
The FLTs are charged at a dedicated battery charging station inside the warehouse. They are returned
to this point for recharging when required.
This area is equipped with mains electricity, compressed air, and water services.
There are posters next to the charging station, giving reminders about safe use of FLTs on the site.
5) B) Rest of the site – 10 MARKS
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The FLTs enter through the rear doors of a trailer, deposit the pallets, and reverse out.
Each bay entrance is fitted with a plastic curtain and, in front of that, a roller shutter door.
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On arrival, goods vehicle drivers are expected to hand in their vehicle keys
Within each loading bay there is a safe area for the goods vehicle drivers to stand while the
bread is loaded onto the goods vehicles.
Outside, separated by bollards, there are dedicated parking bays for goods vehicles to wait.
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There is a one-way system in operation for all vehicles across the site.
Panis workers and visitors must use a separate entrance and exit from the goods vehicles and
silo tankers.
Workers and visitors have a separate dedicated parking area.
There is a straight road with traffic calming measures, such as speed humps, running through
the site.
Ccct camara
5) C)
5) D)
6) A) confined space 20 MARKS
Entrapment in a free-flowing solid - e.g. a grain silo containing wheat or barley where a worker
standing on the top of the grain may fall into hidden voids created by the grain ‘bridging’ inside the silo.
Further consideration must be given to the possibility of undertaking the work without putting workers
into the space.
This is often referred to as a ‘permit to enter’. The permit system must be under the control of a
competent manager and will detail the operating procedures to be adopted.
Provision must be made for safe evacuation of casualties in the event of any foreseeable incidents
Proper PPE (not bulky)
Use of a harness with a rope securely attached to a retrieval line should be considered. The other end
of the retrieval line must be attached to a mechanical device or a fixed point outside the permit space.
A mechanical device should be available to retrieve someone from vertical-type permit spaces more
than five feet (1.5m) deep.
Worker suitability
Competency Requirements of the Workers
Emergency procedures
Lighting
Fire prevention (fire safety)
Access & egress
PPE
Isolation & lock-off
Ventilation and Atmospheric Testing
The foreseeable atmospheres inside the confined space must be identified and the space may then
have to be ventilated before entry is gained to ensure the atmosphere has sufficient oxygen and is
free of contaminants (that might be flammable and/or toxic).
Communication Methods
6) B)
7) A) Comment on how effective Panis is in controlling static build up. 12 MARKS
The process uses many different pieces of machinery made from stainless steel.
Once regular maintenance and cleaning has been carried out on a machine, this is indicated with a
red-coloured tag.
Six electrically-earthed, vertical, 10 metre cylindrical steel vessels (silos) are each able to store up to
60 tonnes of flour and powdered sugar.
The scheduled offloading operation uses a pneumatic conveying system, whereby compressed air
(from an air compressor on the tanker) is used to dilute and blow the flour through connected
pipework, directly to the main storage silo.
This then passes through a coarsely painted steel cartridge filter into the main storage silo.
Some of the drivers usually electrically earth the tanker during unloading.
Ingredients are delivered in bulk 25 tonne loads
The driver liaises with a bakery worker to unload the ingredient at a sheltered discharge point.
Despite training and clear signage on how to perform the task safely
Flour for immediate use is stored in a smaller, alloy steel receiving vessel inside the bakery.
This receiving vessel is equipped with a fine mesh filter.
When necessary, bakers top up the smaller vessel by pneumatically conveying flour from the main 60tonne storage silo through transfer pipework.
From the vessel inside the bakery, the flour is pneumatically conveyed at high speed inside narrow
steel pipework that runs horizontally and vertically along pipe racks, to the respective bread-mixing
machines.
There is a network of interconnected electrical bonding straps attached to the pipework and an earth
grounding point
The factory has several old dust extractors LEV
7) B) how could static electricity control be improved? 10 MARKS
Silo tanker drivers often want the transfer done quickly, due to time pressures.
Despite training and clear signage on how to perform the task safely, drivers tend to increase the flour
transfer rate.
More recently, when left unsupervised by bakery workers, some of the drivers have not always
electrically earthed the tanker during unloading.
Maintenance workers have reported that they are starting to find fragments of metal in the fine mesh
filter.Recently, bakery workers have reported rattling noises inside this pipework and a slower flow rate
in which the flour is being transferred.
From the vessel inside the bakery, the flour is pneumatically conveyed at high speed inside narrow
steel pipework that runs horizontally and vertically along pipe racks, to the respective bread-mixing
machines.
There is evidence of some rusting within this pipework and blockages often occur during this process.
There is a network of interconnected electrical bonding straps attached to the pipework and an earth
grounding point. The humidity in the factory causes these bonding attachments to corrode.
Due to the heat produced in the bakery, bakery workers sometimes keep an external door open for
some fresh air. (Needs better ventilation)
8) A) How would an interlocking guarding system operate to help avoid the dough mixer
accident? 3 MARKS
8) B)