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3.8

Abrasive Selection

Abrasive selection is likely the most difficult decision related to the blast operation. Choice of
abrasive is based on factors such as blast application type, desired finish and coating
requirements, characteristics of object to be blasted, cost and ability to recycle, available
equipment, safety, and environmental constraints.

There  are  many  abrasives  available  that  are  either  natural,  manufactured,  or  processing  by-
products.  Abrasives  are  available in  varying sizes,  shapes,  and hardness.  These characteristics
determine the resulting effect on the surface to be blasted and limitations of its use. The effects
on  the  blasted  surface  are  measured  by  its  degree  of  cleanliness  and  the  surface  profile.
Standards  and  required  levels  of these measurements  are  established by  organizations  such as
Steel  Structures  Painting  Council  (SSPC),  National  Association  of  Corrosion  Engineers
(NACE)  and  coating  manufacturers.  See  Section  12.5  for  contact  information  of  these
organizations.  Use  these  sources  to  obtain  information  regarding  all  aspects  of  surface
preparation and abrasive selection guidelines.

Schmidt® abrasive blasters are designed for high production open abrasive blasting with a wide
range of abrasives. It is the responsibility of the employer and operators to select the proper
abrasive. It is the responsibility of the employer to make certain that the abrasive selected is
safe to use for abrasive blasting.

Critical:

Always obtain the Material Safety Data Sheet (MSDS) for the abrasive to be used.

The  MSDS  provides  the  chemical  makeup  of  the  abrasive.  Do  Not  use  abrasives  containing
toxic  materials.  Refer  to  OSHA  29  CFR  for  acceptable  limits  of  various  toxic  substances  and
additional measures to be taken to protect operating personnel. Always use abrasives containing
less  than  1%  of  crystalline  silica.  Always  use  a  NIOSH  approved  respirator  when  handling,
loading and cleaning up abrasives. Organic substances which are combustible may only be used
in automated blast systems with ventilation that meets OSHA 29 CFR 1910.94.

3.9

Breathing Air Quality

All blast operators must be supplied with and required to use NIOSH approved air-fed
respirators. Breathing air supplied to these respirators must meet Grade D air quality standards
as specified by OSHA 29 CFR 1910.134(i) and the Compressed Gas Association Specifications
ANSI/CGA G-7.1. Consult these specifications when selecting a source of breathing air.

Breathing air must be clean, dry, contaminant-free, and provided at a pressure and volume
specified by NIOSH. Use NIOSH approved air filters on all sources of breathing air. See
Section 3.10.

Breathing air filters do not remove carbon monoxide or any other toxic gases. Use a carbon
monoxide monitor to detect unacceptable levels. Consult OSHA 29 CFR 1910.134(i).

Many  sources  of  breathing  air  are  available  such  as  air  cylinders,  free-air  pumps,  oil-less  air
compressors,  and  oil  lubricated  air  compressors.  The  most  commonly  used  is  the  same  air
compressor  that  is  used  for  the  blast  air  which  most  often  is  oil  lubricated.  Breathing  air
provided  by  an  oil-lubricated  air  compressor  can  contain  carbon  monoxide  and  therefore
requires the use of a carbon monoxide detector (See Section 3.10). Carbon monoxide can be in
the  compressed  air  produced  by  an  oil-lubricated  air  compressor  when  it  is  operated  at
extremely  high  temperature;  therefore,  a  high  temperature  alarm  is  required  to  alert  the
operators when this condition exists.

Oil lubricated air compressors can produce carbon monoxide. Carbon monoxide can cause
asphyxiation and result in death. Use a high-temperature alarm and a carbon monoxide monitor
when an oil lubricated air compressor is used to supply breathing air. Consult OSHA 29 CFR
1910.134(i).