CASE HISTORIES OF THE PERFORMANCE OF EXPOSURE CONTROL MEASURES


Control of exposures to air contaminants is an empirical field, i.e., the majority of its development as a science results from individual efforts made by industry to control hazards to safety and health. Following are discussions of three case histories of metalcasters’ path to air contaminant control.


Case #1: Coremaking


The general coremaking procedure at a metalcasting facility consisted of an automatic sequence of core blowing, gassing, purging and core ejection. Core machine operators sprayed the corebox with parting compound and removed cores from a rollout conveyor. Core finishers, located along core conveyors, cleaned and repaired cores. The coated sand from which the cores were made was prepared on an overhead mezzanine and transported to individual core machine hoppers. The principal sources of exposure were gaseous leaks past core machine seals and dust leakage past the blow seal during core blowing. Besides exhaust- ing the core box, a critical component of this exposure control strategy was a protocol of scheduled inspections and mainte- nance of potential leakage sources (Table A). The ventilation and leakage prevention program was successful in controlling TEA exposures. However, at the time of the evaluation, sand escape past the blow seals was an ongoing issue for improvement.


Case #2: Charge Preparation and Melting


The reduction/elimination strategy to abate the lead exposure hazard in a ferrous foundry, summarized in Table A, involved the ongoing cooperation of both metalcaster and scrap supplier staff. Alternative ventilation of the charge preparation and melting activities represented a prohibitively difficult and expensive way to address the tramp lead situation.


Case #3: Ductile Iron Grinding


The case involved workers at a bank of stand grinders where ductile iron castings are picked up from a table, cleaned on


the grinder, and dropped into a chute on the other side of the grinder. Each grinder is equipped with local exhaust. Exposure assessments (step 1) indicated that silica exposures often exceed the PEL. An investigation (step 2) indicated that dust is mainly from burned in sand on the castings. Grinding reduces a portion of these embedded sand grains to respira- ble dust. Candidate measures for control (step 3) included a) increased grinding wheel enclosure and exhaust flowrate, b) negative pressure respirators (N95 filtering dust masks), and c) air supplied respirators. A review of the candidate control measures (step 4) indicated the following: a) Existing grinder ventilation did not capture the respi- rable dust because the silica particles are entrained in the grinding wheel windage and released when the windage con- tacts the casting. Increased enclosure and exhaust flowrate would not sufficiently increase capture velocity to overcome the wheel windage effect.


b) Negative pressure respirators, properly fitted and worn would be capable of reducing exposures. However negative pressure respirators suffer from several drawbacks, including fit, comfort, facial hair and leakage issues.


c) Air supplied hoods can achieve greater exposure reduc- tion than ventilation or negative pressure respirators, because workers are breathing clean, supplied air instead of partially cleaned or filtered air. Air supplied respirators have mobility limitations but that was not a factor with stationary grinders. Air supplied respirators in addition to existing grinder ventilation, were selected as the best control in this case. None of the candidate measures could effectively address the exposure source, but air supplied hoods could provide the most effective worker protection. After installing the air supplied hoods the foundry found an added benefit of eye and face protection. This case shows how a step wise perfor- mance-based approach can be used to select the best option for control of a respiratory hazard.


Table A. Case History Assessment of Performance-Based Exposure Control Step 1


Step 2


Exposure Hazard Assessment


• Exposure to trimethyl- amine (TEA) gas and respirable crystalline silica (silica) during coremaking at twelve stations.


Sources of Exposure


Phenolic urethane cold box (PUCB) coremaking


• Leakage of TEA and silica from core box seals and seal between core box and sand hopper • Off-gassing from


just-produced cores during core handling and finishing


Charge preparation and melting in a ferrous foundry


• Lead exposure during melting of purchased ferrous scrap


• Purchased ferrous scrap con- tained “tramp” lead in the form of lead-containing bearings and bushings and lead-based paint on scrap


• Tramp lead readily vaporizes and creates airborne lead fume due to lead reaching its boiling point during ferrous melting


34 | MODERN CASTING July 2016


• Establishment and aggressive enforcement of specifications for scrap supply, using chemi- cal analysis where needed, to certify compliance


• Close-capture ventilation of melting furnaces


• Respiratory protection until lead exposure was abated


• Management commitment was critical to the enforcement of scrap supply specifications


• Costly ventilation changes to capture lead fume during melting was avoided by use of scrap specification.


• Close-capture exhaust at the core box


• Distributed supply air at core making stations


• Regular maintenance of core- box seals


• Leakage prevention eliminates/ reduces air contaminant sources


• Close capture ventilation and local supply air prevent air contaminant buildup at work station


• Feedback from core machine operator needed for quick response to occurrence of leaks.


Step 3 Candidate Control Measures


Step 4


Control Method Assessment


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