Journal of Health and Safety at Work

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Introduction: Adherence to the design values and ventilation standards (VS) after installing and also maintaining continuous work of ventilation system with maximum performance throughout its life are amongst the reasons of ventilation systems monitoring. Therefore, the aim of this study was to evaluate performance of local exhaust ventilation system for control of dust by measuring the operating parameters and also to compare it with ventilation standards (VS) and design values.

Material and Method: The present research is a descriptive and cross-sectional study, conducted in three sections of measuring, monitoring and evaluating the operating parameters on hoods, channels and fan of ventilation system based on the current status of the system, documentation (design), and recommended standards (VS). Static pressure, velocity pressure, surface area, and flow rate were measured based on the recommendations of various sources and ACGIH industrial ventilation manual, and the data were compared with the design and recommended values, using the SPSS software version 16.  

Result: The results of paired sample t-test between flow rate and velocities of design and current status, showed significant differences in various parts. Accordingly, the results revealed a reduction of more than 50% in the design duct velocity compared to the current duct velocity, while design duct velocity is 1.3 more than the standard duct velocity of current status, and current duct velocity is about 65% of standard duct velocity.

Conclusion: The reduction and nonconformity of the results of measurements of operating parameters (after a minimum of two decades) with design and standard values are corroborant and sufficient reason for obstructions, abrasions, leaks, imbalance of system ducts and their inefficiency in some branches. Since there is no base line measurements for system (supposing that the system worked with maximum amounts of setup time), one of the reasons for these changes can be attributed to lack of schedule for regular and appropriate maintenance.

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Introduction: Efficiency of hoods for local exhaust ventilation system is influenced by hood geometry, its situation relative to the process and the air volume exhausted by it. The aim of this study was to present a simple and practical method based on the standards for assessment of potential problems of ventilation system in a steel making company.  

Material and Method: In this cross-sectional study, a checklist based on the ACGIH ventilation standards was developed for investigating potential problems related to the three types of hoods in an oxide screen process. This checklist has completed in order to feasibility study of corrective changes in evaluation of the hood hardware parameters. The differences between design and current status to the standards were considered as noncompliance. Finally, differences were analyzed statistically.   

Result: Based on statistical analysis, the average of current status of hoods, plans and design documents and standards were for variables of conveyors downstream enclosure (1.6, 2.38 and 2.41m), vertical distance from hoods to conveyors (0.39, 0.37 and 0.61m), conveyor longitudinal enclosing after hood (1.225, 1.288 and 0.296 m) and hood numbers (18, 17 and 31), respectively. Comparing the results between current status of hoods with plans and design documents showed no significant differences (0. P-value≤ 0.05). But, the results between current status of hoods and design documents with standards have significant difference (0. P-value≥ 0.05). A significant difference  (0. P-value≥ 0.05) revealed between the average of the current status of hoods, plans and design documents and the standards for variables of hood flow (813.3, 2276.9 & 3085.9 cfm) and duct velocity leading to the hoods (2289.3, 5083.5 & 3500 fpm), respectively.

Conclusion: This method can be applicable for the local ventilation systems with extensive pollution sources and hoods. One of the advantages of this method can be easily application of this system, as one of the requirements for delivering ventilation systems from contractors and the use of it for studying potential problems of the hoods that they have standards. Also, by comparing current status of hoods with the design specifications and standards, the mismatches/ unconformities in the lifetime and maintenance process of the system can be understood.

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Introduction: Chemical industries often have risks for the environment and communities, due to the use of complex facilities and processes. Also, in the ammonia tanks, the probability of risk of explosion is high, owing to their specific characteristics. The aim of this study is to evaluate the risks of explosion scenario at the ammonia tank in the Kermanshah petrochemical complex
Material and Methods: To achieve the purpose of this study, the Fuzzy Fault Tree Analysis (FTA) method was used to estimate the probability of reliability in the basic events. In this study, after drawing Fault Tree for identifying basic events, the probability of basic events was estimated by means of expert’s elicitation, and the probability of minimal cut sets was computed through Boolean logic gates.
Results: According to the results, the probability of occurrence of the top event was obtained equal to 0/054997. In the minimal cut set prioritizing, the failing of pressure safety valves identified as the most effective factor in the top event occurrence, and afterward failing the control valves and human errors were identified.
Conclusion: This study indicates that, based on expert elicitation, a fuzzy error tree method can be used to assess the risk of various scenarios in the industry. Overall, in assessing the risk of the explosion scenario in the ammonia reservoir, it was found that some minor defects, and even human error, could be considered as a major contributor to the explosion.