U.S. Department of Labor
Process: Hot Work
Hazard: Over Exposure to Harmful Substances
Hot work in shipbuilding and repair is performed on a variety of surfaces and under circumstances that sometimes require precautions to prevent employee over exposures to harmful substances. Because of the wide variety of materials and coatings used or encountered in shipyard work, material safety data sheets (MSDS) are the best source of information for determining which materials present a potential hazard when heated. If an MSDS is not available (as is often the case in repair work or ship breaking) the surface on which the hot work is to be performed should be tested to determine its composition and that of any coatings that may have been applied.
In an enclosed space, general mechanical or local exhaust ventilation is required for hot work (welding, cutting, or heating) on any of the following toxic metals:
- Zinc-bearing base or filler metals or metals coated with zinc bearing materials (i.e. galvanized pipe)
- Lead base metals
- Cadmium-bearing filler materials
- Chromium-bearing metals or metals coated with chromium-bearing materials (i.e. stainless steel)
The air exhausted from the working space must be discharged into the open air, away from the intake air.
When performing hot work in an enclosed space on metals containing lead as other than an impurity, cadmium-bearing, or cadmium coated base metals, or metals coated with mercury bearing materials, only local exhaust ventilation or airline respirators are acceptable as a means of protecting workers.
Both local exhaust ventilation and airline respirators are required for work on berylliumcontaining base or filler metals in an enclosed space.
General mechanical ventilation onboard a vessel is usually accomplished by fans or air movers which add or remove air in a space in order to maintain the concentration of the contaminant below hazardous levels. The sucker tube is one of the most frequently used methods of local exhaust ventilation in shipyards, and when used properly is one of the most effective. A well positioned sucker tube will remove nearly all of the plume being generated by the hot work at it's source. The tubes can be easily repositioned as the work progresses or as the worker changes position. The most common mistake in using this device is that the welder or burner will place the sucker tube either too far from the plume or place it in a location that draws the plume through the breathing zone.
In landside shops, the natural air flow through open doors, windows, or roof ventilators may be adequate for maintaining safe air concentration levels. It is important to note that air sampling is the only way to be certain that acceptable levels of air quality are being maintained when this type of general ventilation is utilized. It is a safe bet however, that if a blue cloud surrounds the workers head, or fumes seem to be hovering in the breathing zone, ventilation is not adequate.
Hot work performed in the open air on these toxic metals requires the use of respiratory protection. Filter type respirators are most commonly used for this purpose but workers must be trained in their use, and fit tested before being permitted to use them. A comprehensive respiratory protection program must be implemented to ensure that filters are changed when needed and respirators are kept clean. Some shipyards require that respirators be turned in everyday. Other shipyards make respirator filters and wipes for cleaning available to employees at area tool cribs, while another shipyard issues zip lock bags along with respirators so that workers have a clean place to store them. Some shipyards have found it effective to post a respirator-use matrix in the areas where the respirators and filters are issued as a way to ensure that the right type of respirator and filter for the job are issued for use.
Workers performing hot work on bulkheads, decks, or overheads are sometimes unaware of what is on the other side. This is problematic if a painted or insulated surface is being worked on. While the worker may have removed paint or insulation from the area where the hot work is to be done, the other side can present a problem if the material is not removed and begins to smolder or burn. In the case of lead paint, epoxy compounds and some insulating materials this may result in a potential overexposure, not to the worker performing the hot work, but to those workers on the other side of the bulkhead adjacent space. Shipyards employ a variety of methods to try and prevent this occurrence. "No paint mark up," for example, involves identifying and marking areas where hot work will later need to be performed so that no paint is applied until after it has been completed. Masking prior to painting those areas where hot work will be required later is another method employed in some shipyards. Experience has shown that the surest way to prevent this problem is to check both sides of the bulkhead before applying heat.
It should be noted that certain confined and enclosed spaces and spaces adjacent to them will require testing by a shipyard competent person or Marine Chemist prior to entry, and must be certified as "safe for hot work." Additionally, anyone entering spaces that meet this criteria must have a confined and enclosed space training certificate. The specific requirements for entering and performing hot work in confined and enclosed spaces can be found in OSHA standards 29 CFR Part 1915, Subpart B.