CONFINED SPACE - Explosive conditions: grinding, cutting and welding (including pre-heating) from the inside or outside of confined spaces

Purpose
Background
Contributing factors
Action required
Further information

Purpose

The purpose of this safety alert is to provide practical guidance to minimise health and safety risks associated with the danger of grinding, cutting and welding in, on and around confined spaces and compartments such as tanks, containers, vessels and other enclosed structures, which have contained flammable or combustible liquids.

Background

A co-owner of an aluminium fabrication and repair workshop was fatally injured by an explosion while using welding equipment on a boat. Other incidents have occurred in which workers have conducted hot work on fuel tanks and containers causing explosions that have led to fatalities and serious injuries.

Contributing factors

Vapours
Flammable liquid vapours (e.g. petrol, ethanol and solvents) can cause an explosion when confined, for instance in a container, vessel or void, and ignited. Combustible liquids (e.g. diesel fuel and oils) can behave like flammable liquids when they are heated, by generating vapours that, when confined, can also cause an explosion when ignited.

Ignition sources
Activities such as grinding, hot cutting and welding, or even hot surfaces caused by these activities, are potential ignition sources for a flammable atmosphere. These activities can provide enough energy to ignite a mixture of flammable vapour.

The blast wave and fireball produced by such an explosion can cause significant property destruction and personal injury or death.

Action required

The following control measures will need to be taken to reduce the likelihood of injury from grinding, cutting, and welding (including pre-heating) while working on the inside or outside of a confined or enclosed space, compartment or vessel where flammable vapours may exist:

• Analyse the hazards: identify the scope of work, potential hazards (e.g. flammable atmospheres or generation of toxic fumes) and risk control measures.
• Monitor the atmosphere: perform atmospheric testing for flammable or combustible gases, oxygen deficiency and for toxic gases before and during the activity, even in areas where a flammable atmosphere is not anticipated.
• Test the area: check for hidden voids or compartments that may share the same airspace. This may be a hidden source of flammable vapours. If tests demonstrate that flammable or combustible gases are present, these must be eliminated by cleaning, ventilating and/or inerting the space before hot work activities can begin.
• Check there is no unidentified source of flammable liquids or residues that, when heated, can create an explosive atmosphere.
• Use written permits: ensure that safe work practices are followed, including all hot work permitting procedures in areas where flammable vapours may be present. This involves identifying the work to be conducted and the necessary precautions to be taken.
• Welding processes may generate toxic materials (e.g. ozone and metal fume) that may require additional risk control measures to ventilation, such as respiratory protection, particularly when conducted inside enclosed areas.
• If there is a possibility of fire, always have a fire watcher with appropriate fire fighting equipment on hand.

Getting the job done safely should always be your first consideration.

All hazards should be thoroughly assessed before anyone carries out the work. Evaluate the job requirements thoroughly and implement appropriate safety precautions. This process will reduce the risk of an incident and fatality.

Photograph 1: Explosive conditions: grinding, cutting and welding (including pre-heating) from the inside or outside of confined spaces

Hose whip on concrete pumps

Purpose
Background
Contributing factors
Action required
Further information

Purpose

The purpose of this alert is to highlight the hazards and risks to workers caused by hose whip on concrete pumps.

'Hose whip' describes the uncontrolled and rapid motion of the flexible rubber hose on the end of a concrete placement boom or other concrete delivery line.

The following information is provided to assist employers, self-employed people, principal contractors, clients and project managers to meet their obligations under the Workplace Health and Safety Act 1995.

Background

A Queensland worker was fatally injured after being knocked over by a hose, which started to whip at the end of a mobile concrete placement boom. The worker fell and struck his head on a fixed steel structure. During the incident, two workers (one of whom was fatally injured) had been attempting to hold the hose horizontally.

Contributing factors

Persons can either be injured as a result of being struck directly by the whipping hose itself or being knocked over and hitting the ground or an object.

A hose whip can occur during the concrete pumping operation itself or when the line is being cleaned out. In either case, hose whip can be especially violent when air enters the line and becomes pressurised by the pumping process.

Action required

The likelihood of hose whip can be greatly reduced by the selection of suitable plant and safe systems of work. While the risk of hose whip can be reduced, additional precautions need to be taken to reduce the likelihood of injury.

To minimise the likelihood of injury from hose whip the following safety precautions are to be addressed:

• Only pump concrete that is a pumpable mix as specified by the concrete supplier. Other mixes of concrete can block the line and cause hose whip.
• Do not let the concrete solidify in the line because this will cause blockages. The concrete needs to remain in its plastic state.

Example 1: line hand gently guiding hose and signalling to pump operator.	Example 2: line hand and worker operating concrete vibrator.

• Use well trained, competent operators to pump concrete (see examples 1 and 2).
• Start the pump up slowly to reduce the likelihood of hose whip.
• Never attach metal fittings to the free end of the rubber delivery hose (see example 3).
• Persons not involved in the concrete pour should be excluded from the delivery hose area.
• Never try to stretch the delivery hose if it doesn’t reach the pouring location (see example 4).

Example 3: do not use metal fittings on end of delivery hose.	Example 4: workers stretching hose for additional reach. This is unsafe work practice.

• Workers should always wear appropriate personal protective equipment, including hard hats.
• Good housekeeping needs to be maintained around the work area to reduce the likelihood of tripping.
• The delivery hose on a boom pump should hang close to vertical and only be guided by the line hand. If the boom is not long enough to reach the concrete pour area, a larger boom should be used or the concrete pump should be moved closer to the job.
• Do not let more hose hang from the boom than that allowed by the boom manufacturer (see example 5). Normally a maximum of five metres of 125 mm diameter hose can be suspended from the hose (in some cases this can be less).

Example 5: too much hose hanging from boom.	Example 6: end of delivery hose is folded over using wire to prevent concrete falling out.

• Do not allow concrete to drop out of the hose when pumping is stopped, as this can allow air to enter the system. The hose can be folded over to prevent concrete dropping out (see example 6).
• Always ensure the line hand has an adequate sized area to stand on (the width of the working surface should be 450 mm or greater). The line hand should not stand on block walls or next to unprotected edges (see examples 7 and 8).

Example 7: pouring concrete into column form. Good access is provided.	Example 8: poor access for line hand. Access is too narrow and edge protection is not provided.

• Monitor the level of concrete in the hopper to avoid air getting sucked into the pump system. Ensure a separate person to the line hand is in position to view the hopper. This will normally be the pump operator.
• Make sure safe work procedures are adopted for clearing blockages.
• Preferably clean out the concrete line with water instead of air.
• When there are no other options but to clean the pump line out with air, secure the end of the steel line and have an exclusion zone. All reducers and the rubber hose must be removed from the end of the delivery line. A ball catcher should be fitted to the end of the steel pipe. This will contain the blow out plug (i.e. sponge) as it is ejected from the line.

Further information

Further information is available in the Concrete Pumping Code of Practice 2005 or by calling Workplace Health and Safety Infoline on 1300 369 915.

Storage and handling of sheet materials

Background
Contributing factors
Action required
Further information

The purpose of this alert is to highlight the hazards and risks from the storage and handling of sheet materials stacked on their edges.

Background

A worker was fatally injured after being struck by falling solar collectors for hot water systems, which were stacked on their edges. Other incidents have occurred involving sheet materials stacked on their edges falling due to inadequate support when being moved.

Sheet materials may include:

• glass sheets, windows or shower screens
• sheets of stone or marble (e.g. kitchen bench tops)
• plywood, MDF, chipboard, plasterboard, doors or other building products
• prefabricated frames and trusses
• reinforcing mesh and steel plate
• solar cells (e.g. photovoltaic cells and solar collectors for hot water systems).

Contributing factors

Workers or others in the immediate vicinity of stacked sheet materials are at risk of being crushed, trapped or cut by falling sheets of material. Workers may also sustain musculoskeletal injuries when they are required to manually balance stacks of sheets during sorting and handling.

The risk of severe or fatal injuries is high when materials, which have been stacked on their edges, are being handled or moved and the sheets are not adequately supported by suitable racking or transport frames.

Action required

Where it is necessary to store materials on their edges, the stability of the stacked load must be accounted for in the design of the support system. An item is in a stable (balanced) position when it is restrained with the centre of gravity directly above the supporting edge. If the centre of gravity is inadvertently moved outside the supporting edge, the item will become unstable (see diagram 1).

Diagram 1: Balanced and unbalanced loads relative to its centre of gravity

If sheet material of any kind is to be stored or handled, controls must be in place to safely support them. Stacking of sheet materials without an adequate restraint is potentially very dangerous.

An obligation holder, whose workplace includes areas where goods are stored on their edges, must implement controls to eliminate or minimise the risks of death or injury. This may be addressed by using a combination of:

• engineering controls, such as a rack or transport frame, to securely store, cradle, lift, transport and restrain the sheets
• safe systems of work (e.g. use of mechanical lifting equipment whenever possible, regimes for maintenance, inspection and testing of all racking and lifting equipment)
• adequate training and supervision of workers engaged in the work.

Where materials are stored in strapped bundles the risk of injury when the strapping is cut must also be assessed.

When strapped bundles are opened for the first time, purpose-designed support frames or temporary restraint should be provided to ensure the load does not become unstable.

Sheets of material of more than one type or size should never be stacked against walls or in areas without adequate support. Storage systems should separate sheets of different types and sizes to simplify the sorting task.

The support system needs to be designed for forces resulting from unbalanced loads. Examples of racking and storage systems for sheet materials are shown in photographs 1, 2 and 3. 

Photograph 1: An example of storage system for large panels	Photograph 2:An example of storing panels of varying sizes	Photograph 2: Example of stacking frame

Further information

For practical advice on managing exposure to risk when using plant, visit www.worksafe.qld.gov.au or call the Workplace Health and Safety Infoline on 1300 369 915.