1. (1) You must install adequate ventilation systems in blast cleaning enclosures that are able to do all of the following:

   1. (a) Control concentrations of airborne contaminants below the permissible exposure limits that apply;
   2. (b) Provide a continuous inward flow of air at all openings in the enclosure during blasting operations;
   3. (c) Minimize the escape of dust into adjacent work areas;
   4. (d) Maintain visibility in blast cleaning rooms and cabinets;
   5. (e) Rapidly clear dust from the air after blasting stops;

   6. (f) Discharge exhaust so contaminated air does not do either of the following:

      1. (i) Present a health hazard to any worker; or
      2. (ii) Reenter buildings in harmful amounts.
2. (2) You must make sure ventilation systems are designed and operated so employees are not exposed to excessive air velocities.

3. (3) You must make sure make-up air systems do not interfere with the effectiveness of the exhaust system, and are designed to do both of the following:

   1. (a) Replace exhausted air in ample quantities;
   2. (b) Temper make-up (supply) air when necessary.

4. (4) You must do both of the following before opening the blast cleaning enclosure:

   1. (a) Turn the blast off;
   2. (b) Run the exhaust system for a sufficient period of time to clear the air of dust particles.

5. (5) You must follow the requirements in Table-2, Blast Cleaning Enclosures.

   Table-2: Blast Cleaning Enclosures

   If you have	Then make sure
   Air inlets and access openings	They are either baffled or arranged so the combination of inward airflow and baffles minimizes both of the following:
   	- The escape of abrasive or dust particles into adjacent work areas.
   	- Visible spurts of dust
   Small access openings where dust might escape	Slit resistant baffles are installed in multiple sets at all small access openings, and do both of the following:
   	- Regularly inspect them
   	- Replace them when needed
   An observation window in enclosures where hard, deep cutting abrasives are used	The window is made of safety glass protected by screening
   Notes:
   • Hard, deep cutting abrasives may shatter normal glass.
   	• If the safety glass shatters, the protective screening will help contain the glass and protect employees from cuts and lacerations.
   Small operator access doors	They are flanged and tight when closed, and open from both inside and outside the enclosure.
   	Note:
   	If you have a small operator access door and a large work access door, the large work access door may open or close from the outside only.

   References:	For more information on:
   	1. Air velocities, refer to the following:
   	a. The latest edition of Recommended Industrial Ventilation Guidelines (ACGIH);
   	b. NIOSH 1976 Industrial Ventilation;
   	2. Exit routes, go to the Safety and health core rules, WAC 296-800-310.

[Statutory Authority: RCW 49.17.010, 49.17.040, 49.17.050, and 49.17.060. WSR 17-18-075, § 296-818-30010, filed 9/5/17, effective 10/6/17; WSR 06-12-074, § 296-818-30010, filed 6/6/06, effective 9/1/06.]