Document ID: OSHA-2010-0001-0077
Agency: osha
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-11-12T05:00Z

MARITIME INDUSTRY – Ventilation for Welding and Allied Operations in
Shipyard Employment, 29 CFR 1915

Ventilation Requirements

(1)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. 

(2)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.

(3)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. 

(4)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.

(5)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. 

(6)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

(7)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

(8)Welding, cutting or 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.

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  

(9)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. 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

(10)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

(11)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.  

COMMENTS

General Comments

The committee rearranged the paragraphs from the initial document to
make it flow better. The comments below provide comments on the specific
paragraphs in the document above. Each paragraph has been numbered to
match the comments.

The committee felt that the inclusion of pictures throughout the
document backing up the statements would add to the effectiveness of the
whole document both by making it more visually attractive and backing up
some of the explanatory material. 

Paragraph 1.

Possibly include definitions of local exhaust and dilution ventilation
or photos or diagrams.

Suggest reworking paragraph as follows:                                 
                  Mechanical exhaust ventilation must be provided in the
ship repairing, shipbuilding, and shipbreaking industries, when welding,
cutting, and burning operations take place in enclosed spaces. 
Mechanical exhaust ventilation can be accomplished by providing either
local exhaust ventilation or dilution ventilation

Add pictures of ventilation system with hood

Paragraph 2/3.

Suggest reversing paragraphs 2 and 3 as follows to make the flow better:
               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, and
clear of other sources of intake air.  Local exhaust ventilation [shall
or should] [unless in regulation then 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 prevent air flow from behind the hood.  Use of a flange 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.

Paragraph 4

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

Paragraph 5

Suggested rewording.                                                    
                                   When setting up mechanical dilution
ventilation, there are several points to keep in mind.  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 funneled into an exhaust system as rapidly as possible.
This will keep contaminants out of the breathing zone of the worker and
reduce the level of air contamination.

Paragraph 6

Replace the first sentence with: The capacity of dilution supply and or
exhaust ventilation provided depends on several factors:

The sentence stating that oxygen should not be used for ventilation etc.
should be a highlighted box or some other method which emphasizes the
importance of this hazard.  

Paragraph 7

No comments.

Paragraph 8

Suggest adding the word torch in the first sentence. Welding, cutting or
torch heating…

While this section is essentially a direct quote of the OSHA regulations
it is confusing. Suggest rearranging it in a manner to make the intent
clearer. Use of a table may help clarify this area. 

Paragraph 9

While this section is again a restatement of the current regulations a
suggestion to make the paragraph flow better is as follows: 

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.  Employees working on the materials
listed above in the open air must be protected by appropriate filter
type respirators.  Other employees exposed to the same atmosphere as the
welders or burners must be protected in the same manner.

Are there any other materials which require a welder to have the same
level of protection? 

Should PCB impregnated materials be included in this section for PPE
requirements? 

Paragraph 10

Suggest a slight rewording to make it flow better. Once again the
committee recognizes that the current statement is a copy of the
existing regulations. 

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 §1910.134.  These requirements are
designed to protect against dangerous concentrations of nitrogen dioxide
that can potentially be generated.

Paragraph 11

The committee suggests that the words “unsafe accumulation of
contaminants” be defined or worded differently to explain what is
meant by this statement.