Pulling Sled Safety(Presented at Alcester on 9 Feb 2008)

Geoff Frackelton Principal Specialist Inspector,

Mechanical Engineering North West

Content

• Part 1 – Basic concepts of Risk Assessment.

• Part 2 – Legal Requirements

• Part 3 – Gt Eccleston, Lessons Learnt and Future Recommendations

Part 1 - Basic concepts of Risk Assessment.

Design, Construction and

Operation risk assessments

Definition of a Hazard:• Something with the potential to cause

injury or damage to health. • Always exist (Potentially) unless we

choose to stop doing the activity altogether.

Risk is defined as

‘THE LIKELIHOOD AND CONSEQUENCE OF AN EVENT’.

Example • Driving a car creates a hazard of crashing and

going through the windscreen.• Likelihood is high on today's roads but lower on

say private land.• The consequences of that would be pretty

serious and would cause harm

How can we achieve a tolerable risk level ?Controls such as:-1. Stop driving, eliminates the risk (the potential

hazard is still there)2. Better driver training to reduce likelihood3. Drive slower to minimise the consequences.4. Controls such as seat belt, safety glass, air

bag.5. Constant Monitoring through MOT

What is a Risk Assessment?

1. A structured way to identify hazards. 2. Use 5 steps to RA by HSE. 3. RA should not be bureaucratic. In fact it

doesn’t even need to be written down (unless you employ 5 or more people).

4. RA should be useful.5. RA doesn't need to cost £ thousands.6. RA requires somebody who understands

sleds and can develop control measures.

Failures and effects of a passenger lift • Control failure high likelihood but only

leads to inconvenience, low conseqeuces.– Fit emergency phone/instructions– Adequate lights with battery backup

• Service brake failure low Likelihood but could lead to minor injury so medium consequence– Failsafe brakes, regular inspection– Fit emergency brakes

• Rope failure low likelihood but could cause death so high consequences.– Fit duplicate ropes with f.o.s of 4 times.– Regular Inspections– This is the ultimate protective device so high

risk item.

Part 2 – Legal Requirements

Sled Owners duties under PUWER 98

• Inspection at regular intervals to detect deterioration (Separate to pre event inspections by officials)

• Inspection varies from a simple visual inspection to a detailed inspection with dismantling and or testing.

Inspection Cont.d

• As a minimum, inspect safety related parts e.g brakes, limit switches, warning devices etc.

• Inspection should be carried out by people who have the necessary qualifications, experience and skills.

• Inspection frequency based on how quickly the sled is likely to deteriorate and give rise to a risk.

• Inspection results should be recorded and kept until the next inspection.

All sleds should be maintained in an efficient state, in efficient working order and in good repair.

Maintenance should include 3 elements:

• Planned preventative

• Condition based

• Breakdown

• (No legal requirement to keep a maintenance log but recommended and if kept it should be up to date).

Help

• Refer to Farm vehicle health check scheme produced by BAGMA.

• Refer to Is your work equipment legal, PUWER 98 on inspection produced by BAGMA.

• Refer also to other guidance on PUWER

• Refer to HSE website etc.

Part 3 – Gt Eccleston, Lessons Learnt and Future Recommendations

Key Facts From Incident at Great Eccleston

• Weight box ran away

• Weight box was not stopped

• Weight box was ejected from the sled

What did this highlight ?

• Numerous single components can fail to cause a run-away weight box.

• A run-away weight box can be difficult to stop.

How can we minimise risk of single component failure leading to incident ?

• Use reliable components that are adequate for the duty.

• Use failsafe components as much as possible, e.g spring brake chambers.

• Duplicate components, (dual circuit brakes on a family saloon).

How can we minimise risk of single component failure leading to incident, Contd ?• Design sleds in accordance with industry or

sport best practice, i.e – British Standards– Regulations– Known technology, – Current Sled rules.

• Need to demonstrate compliance with recognised standards to satisfy:

• Officials of the sport• Enforcing Authorities• Yourselves

• Could have central inspection body or self certification against standards. (e.g CE)

Measures to minimise the consequences if a box drive component fails.

Two emergency stops, • One for the tractor engine kill • One for everything else to minimises risk

that driver will not use for fear of blowing tractor up.

• Reduce operator error by having simple clear controls (consider standardising).

• Un-obstructed view of weight box from cab.

Would the weight box brakes stop the box if it ran away?

• Ensure driveline brakes are adequate (assumes the box will remain engaged to its drive system).

• Consider over speed monitoring to keep box speed under control. Ke = 1/2mV2

• Automatic detection of box movement relative to wheels again to keep box speed under control.

The Ultimate Stop (seat belt/air bag)

• Adequate end stop determined by a structural engineer or else type tested and built to a standard.

• Buffers or shock absorbers.• Angle chassis downwards• Ensure box is adequately retained on

chassis.• Ensure weights are adequately restrained

in box.

A Physics Lesson

•Initial velocity is mega fast

•Velocity relative to the moving sled = 0

•Acceleration = Deceleration of sled. This is created by braking/friction pan and is a constant.

•Distance to buffers is a constant.

Final velocity = V and is a function of acceleration and distance

(v2 = u2 +2as)

Case 1 - Very fast modified tractor

•Initial velocity is mega slow

•Velocity relative to the moving sled = 0

•Acceleration = Deceleration of sled. This is created by braking/friction pan and is a constant.

•Distance to buffers is a constant

Final velocity = V and is a function of acceleration and distance (v2 = u2 +2as)

Case 2 - Very slow mini puller

For the mathematicians

• v2 = u2 +2 as• Where:• U =constant• A = constant• S = constant

• Therefore v must be a constant.

Therefore !!

• Initial sled speed is irrelevant.

• Impact speed would only be higher if:

• the box was already accelerating (virtually impossible in reality)

• Braking efficiency was improved.

• Box weight increased.

Examples of current best practice

Requirements of the ETPC sled rule book (1/1/06 to 1/1/08). • Paragraph 5.e, Box drive train must be equipped

with a brake capable of stopping a fully loaded weight box at maximum speed.

• Paragraph 6.e, Braking system must also be failsafe.

• Paragraph 10.j, each sled has to have a system which observes the box movement according to the movement of the ground wheels. If the speed of ground wheels disagrees with the speed of the weight box emergency shutdown has to be activated.

Examples of current best practice

Requirements of the ETPC sled rule book (1/1/06 to 1/1/08). • Paragraph 10.i, and Paragraph 1 f, if a kill switch is

applied box brakes and all driveline brakes have to be applied together. Also Paragraph 8 a, A fail safe emergency system separate from normal sled controls that can be activated by use of one control on operators station that activates the following systems:

» Applies a Kill Switch» Applies all four emergency brakes on drive axles» Applies drive train brakes» Applies weight box brakes on sled frame rails.» Applies emergency pan drop» Applies pan push down device

» It is recommended to activate emergency shutdown systems by

kill switch activation.

Examples of current best practice

Requirements of the ETPC sled rule book (1/1/06 to 1/1/08).

• Paragraph 6.g the weights in box to be secured in a way that they could not move in the box or come out of the box in any situation.

• Paragraph 7.c, In front of the rails 2 sets of stops for the box each stop strong enough to stop a fully loaded box free wheeling at any speed.

Summary

• Need a risk assessment.

• PUWER for inspection and maintenance plus other requirements

• Work to some sort of common objective with safety related issues.

Thanks for Listening