In 2014 a significant number of fatal accidents involving large tyre inflation occurred. This prompted the Health and Safety Authority to issue a safety alert to highlight the need for safe procedures during large tyre inflation in all work sectors.
First of all we are going to look at the dangers that are associated with large tyre inflation.
Dangers of Explosive Energy Stored In Tyres
A surprisingly large amount of energy is stored within inflated tyres. For example, the sidewall of a typical commercial vehicle tyre typically has over 34 tonnes of force acting on it.
This force is well below the typical failure point that tyres are designed to withstand but if the tyre is damaged or used while flat (run flat), or significantly under-inflated, they may fail due to weak points that are created.
The force contained within a tyre can then be released explosively if the tyre fails and can result in a destructive air blast and the projection of tyre particles are a very high speed. These types of tyre explosion have led to numerous deaths.
Risk of Failure
Removal, replacement and inflation of tyres is an extremely common practice, so it may seem a simple task, but, if you think about it, If something goes wrong, such as the tyre failing, it can cause serious injury and even death from:
- Explosion of the tyre or disintegration of the wheel during inflation.
- Manual handling of the tyre and wheel.
- Collapse of an elevated vehicle.
Cuts and splits should be clearly visible by inspection and there are also industry standards and measures on whether a repair should be attempted or the wheel scrapped.
This said, there could still be damage to the internal steel or textile cords may not be obvious with a visual inspection.
This internal damage may not become obvious until the tyre is re-inflated and a bulge occurs in the wall of the tyre around the weakened point. The extra force placed on the adjacent cords can cause them to break or snap in quick succession, until the casing splits apart, which can often happen in a violent manner. This is commonly known as a ‘zipper-failure’.
To Reduce the Risk of Violent Explosion
Something that is very important to do, before deflating a tyre, is to check the pressure and chalk the reading on the tyre wall. One thing to keep in mind is that low tyre pressure may have caused tyre damage due to stress on the tyre wall.
Here are some points you remember when deflating or inflating a tyre:
- Do not inflate any tyre that has been significantly under-inflated until it has gone through thorough tests to check its integrity. Examine wheels and tyres (externally and internally) for any signs of damage, such as cracks, ‘marbling’ (black lines), bulging, soft spots or exposed steel cord. If any of these are present or if you are in doubt, DO NOT re-inflate the tyre.
- Stay outside the likely explosion line, when re-inflating a tyre. See figure 1.
- Watch and listen for any signs that might indicate a zipper failure. If you suspect a problem, do not approach the tyre to deflate it. Instead you should use the quick-release connection at the operator’s end of the air hose.
Personal Protective Equipment (PPE) for Tyre Inflation
In order to reduce and prevent and unnecessary injury to your body and/or eyes, the following personal protective equipment (PPE) should be worn, as a minimum, when working with tyres.
- Correct safety shoes (normally thick, steel toe capped boots)
- Appropriate eye protection (safety glasses or goggles)
Working With Tyres on Commercial Vehicles and Oversized Tyres
When it comes to inflating larger, well-based (single-piece) tyres above 15 psi, extra precautions need to be taken as the larger tyres have the potential to store more energy that can be released if the tyre fails. This also includes some light tyres which are inflated to around 70 psi. They have the potential to cause serious injury if they fail.
The extra measures include using an appropriate restraining device such as:
- A strong, firmly-secured tyre inflation cage. You can also line this with a mesh to help retain debris if the tyre fails. If this cage can be fixed into a position, it may be helpful to mark the ‘danger zone’ on the workshop floor as a reminder to the operators. See Figure 2.
- A secured horizontal stool and associated clamping mechanism. This is similar to that in figure 2, but now the tyre lies horizontal. See Figure 3.
- A portable restraint. An example of this would be a lightweight cover that encloses the whole tyre and wheel rim. This may be useful for off-site repairs. In the event of an explosion the fabric contains projected debris. One limitation to these is that they need to be replaced in the event of a tyre explosion.