Hose safety: the right mix
Wednesday, 13 December, 2006
When incompatible parts are used together and hoses come loose from their fittings, the results can be devastating on workers and the surrounding environment. Add a confined space to the mix and it can become fatal.
A number of tragic incidents over the past couple of months in the mining industry have highlighted just how important safety is when it comes to installing and maintaining hoses.
This issue is not just limited to mining though, as hose technology is used across a broad range of industries. Product manager hydraulic hose and fittings at Parker Hannifin, Gary Howes told Safety Solutions that the issue of hose safety is often raised in regard to mining, as particular care should be taken where the interface between the hoses and people are close and direct and there is no shield or guard between the two.
"Mining (particularly long wall), water blasting, forklifts and backhoes in particular have hoses and people very close together, often with little protection in the case of a failure."
So just what can go wrong when it comes to working with and around hoses? Howes describes two major types of hose failure that can pose a risk to safety.
"The end blowing off. This causes the remaining portion of the hose to 'whip' about until flow stops and allows the medium being conveyed through the hose to escape," he said. "If the medium is a gas, its expansion can cause this to be extreme. Where the medium is a liquid, it can be hot or corrosive, leading to further risks.
"This type of catastrophic failure can also generate further risks. Where the hydraulic pressure was holding a load, the failed hose will cause hydraulic pressure to be lost, and this load is no longer supported."
The second major type of hose failure is described as 'pin holing'. "This involves a small leak in the casing of the hose, which allows a fine stream of the medium contained to be released from the carcass under high pressure," Howes says.
"This fine stream can be extremely hot, cause fires or cause oil injection injury where people are close enough to the problem. This type of injury is extremely painful and can cause gangrene or death."
This is by no means a new issue when it comes to safety and there are a number of standards that relate to hoses and their fittings.
According to Howes, one of the most important steps in ensuring hose safety is to use the right product for the job at hand.
Some standards go as far as to stipulate certain products for particular applications. In these cases, it is always safest to follow the guidelines to the letter. For example, AS/NZS 1869 covers approved hoses for use with gas and AS 2660 for use in mining.
"AS3791 is the base standard for hydraulic hose and fittings and implies that 'the hose and fittings should be a matched system. That is, where the testing carried out, as set out in the standard, is done with hose and fittings designed to work with one another'," Howes says.
He warns that dangerous conditions can arise when products from different manufacturers are mixed together. Even though both manufacturers' products may comply with the relevant standard, they could be on the opposite extremes of these tolerances and not pass the appropriate tests as an assembly. This type of product mixing, without appropriate testing, often leads to fitting blow-off.
There are some standards that refer to the safe use of a hose in a particular industry such as water jetting (AS4233.1:1999) or steam cleaning (AS2284:1979), but in general, standards rarely set out the safety regarding the use of the hose.
Specific safety guidelines largely come about as a result of the actions of people that are committed to safety, Howes says.
He also points towards the soon-to-be-introduced MDG41, a NSW Department of Primary Industries Design Guideline that is extensive and goes well beyond a standard.
Howes believes that when this type of document is properly implemented on a site, it contributes dramatically to the levels of safety experienced.
At the end of the day, though, standards and guidelines are not mandatory. When a workplace accident does occur, businesses could still find themselves being judged against the standard, but Howes believes that many industries are not complying with these guidelines as a minimum for safety.
"Industries such as mining (particularly coal) are very committed. Other industries sadly are not, and this is often caused by ignorance as to the existence of suitable standards.
"This issue is difficult, as standards are a guideline only, and unless legislated, there is no obligation for compliance unless it forms part of other legislation. However, it should be noted that while it may not be mandatory to comply with a given standard, if an accident was to occur due to lack of compliance, due care and diligence would be difficult to defend."
Perception of danger is often a hurdle when putting adequate safety systems in place, and according to Howes, it is essential for people working around this equipment to realise the potential danger contained in a hose.
"Most people's only experience with a hose is one that is used in the garden where cool water is conveyed at a pressure low enough to be stopped by placing a finger over the end. Hoses in industrial applications are far more dangerous. Today's hoses can carry pressures of 42.0 MPa (420 bar/6000 psi) plus, in sizes over 50 mm.
"The mediums being carried in them are often hot and flammable. Failures can result in injuries such as oil injection, burning, fire. There's also the environmental damage from the escaping medium.
"Whipping hoses can cause serious injury or death. Respect of standards and guidelines should start to be reflective of this potential danger to people, property and the environment."
Vessels such as pipes and valves that contain tremendous hydraulic pressures are heavily built, bolted and welded. Hoses contain the same levels of pressure and within the same circuit, the hose cannot be welded or bolted to its end fittings, says Howes.
Instead, the circuit must rely on appropriate and accurate assembly to hold the rubber and metal parts together.
"Fine tolerances must be followed for this to work properly, hence the 'matched system'. In addition to this, unlike other vessels, the hose has to be as compact as possible and flexible, creating areas of potential weakness and fatigue.
"It is only when looked at and respected as a flexible pressure vessel with often massive potential energy, and less like the garden hose, that safety with hoses will be improved."
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