MARITIME INDUSTRY – Ventilation for Welding, Cutting and  Torch
Heating in Shipyard Employment, 29 CFR 1915

Ventilation Requirements

In the ship repairing, shipbuilding, and shipbreaking industries,
welding, cutting, and burning operations must be provided with
mechanical exhaust ventilation.  Mechanical exhaust ventilation can be
accomplished by providing either local exhaust ventilation or dilution
ventilation. (Possibly include definitions of local exhaust and dilution
ventilation or photos or diagrams)

Local exhaust ventilation must consist of freely movable hoods intended
to be placed by the welder or burner as close to the work as
practicable.  The hood should be provided with a flange that provides a
barrier to unwanted air flow from behind the hood.  Use of a flange can
achieve either of two positive effects.  It can decrease the volumetric
flow rate required to achieve a given capture velocity at a given point,
or it can increase the velocity achieved by a given flow rate at a given
point.

Unlike dilution ventilation, local exhaust ventilation captures and
removes air contaminants at their source before they are dispersed in
the workplace environment.  The system must be of sufficient capacity
and so arranged as to remove fumes and smoke at the source and keep the
concentration of them in the breathing zone within safe limits. 
Contaminated air exhausted from a working space must be discharged to
the open air, or otherwise clear of the source of intake air.  In
addition, exhaust openings should be located as close as possible to the
source producing the contamination. 

Dilution ventilation must be of sufficient capacity and so designed to
maintain welding fumes and smoke within safe limits.  Dilution
ventilation refers to the dilution of contaminated air with clean air. 
This technique dilutes airborne contaminants by circulating large
quantities of air into and out of the work area.

When using dilution ventilation, there are several points to keep in
mind.  To keep contaminants out of the breathing zone of the worker and
reduce the level of air contamination, the fresh air supplied to the
workspace should first pass through the worker’s breathing zone, then
across the workspace where the contaminants are generated and into the
exhaust system as rapidly as possible. 

The amount of dilution ventilation depends on several factors:

the size of the space in which welding or cutting is done, especially
the height of the overhead;

the total number of employees performing hot work within the space

the hazardous chemical or physical agents produced by the welding or
cutting.

Oxygen must not be used for ventilation, comfort cooling, or blowing
dust or dirt from clothing, or for cleaning the work area.

Welding, Cutting, or Heating of Metals in Confined Spaces

Either local exhaust ventilation or mechanical dilution ventilation, as
described above, must be provided whenever, welding, cutting, or torch
heating is performed in a confined space.  If sufficient ventilation
cannot be obtained without blocking the access, employees in the
confined space must be protected by airline respirators, and an employee
on the outside of the confined space must be assigned to maintain
communication with those working within it and to aid them in an
emergency. 

Welding, Cutting, or Heating of Metals of Toxic Significance in Enclosed
Spaces

Welding, cutting or (torch) heating in any enclosed space on a vessel,
or vessel section involving the metals specified below must be performed
with either local exhaust or mechanical dilution ventilation that
ensures that employees are not exposed to hazardous levels of air
contaminants:

zinc-bearing base or filler metals, or metals coated with zinc-bearing
materials;

lead based metals  

cadmium-bearing filler materials; and

chromium-bearing metals, or metals coated with chromium-bearing
materials.

(PCB impregnated materials) 

When employees weld, cut, or torch heat any of the following materials
in an enclosed space in a vessel or vessel section, they must either be
provided with local exhaust ventilation, or protected by airline
respirators.

metals containing lead, other than as an impurity, or metals coated with
lead-bearing materials;

cadmium-bearing or cadmium coated base metals;  

metals coated with mercury-bearing metals; and

beryllium-containing base or filler metals.  Note: Because of its high
toxicity, work involving beryllium must be done with both local exhaust
ventilation and airline respirators in an enclosed space.

Welding, Cutting, or Heating of Metals of Toxic Significance in the Open
Air  

Employees working on the materials listed above in the open air must be
protected by filter type respirators.  Employees performing such
operations on beryllium-containing base or filler metals must be
protected by airline respirators, in accordance with the requirements of
§1910.134 on respiratory protection. (Any other materials?)  Other
employees exposed to the same atmosphere as the welders or burners must
be protected in the same manner as the welder or burner.

Inert-Gas, Metal-Arc Welding in Enclosed or Confined Spaces

When inert-gas metal-arc welding is being performed on stainless steel,
local exhaust ventilation must be provided that consists of freely
movable hoods intended to be placed by the welder or burner as close to
the work as practicable, or the employees must be protected by airline
respirators,  in accordance with the requirements of §1910.134 on
respiratory protection.  These requirements are designed to protect
against dangerous concentrations of nitrogen dioxide that can
potentially be generated.

General Welding, Cutting, and Heating

Welding, cutting and heating not involving the conditions or the
materials described above may normally be done without mechanical
exhaust ventilation or respiratory protective equipment.  However, where
unusual physical or atmospheric conditions create an unsafe accumulation
of contaminants, suitable mechanical ventilation, or respiratory
protective equipment must be provided.  

Recommendation: Add pictures to the document. 

