# Material Composition Testing Related to Measurement Instrument Enclosure Design and Safety
## 1 Introduction
Despite these contributions, research specifically addressing the horizontal burning behaviour (HB test method) of insulating materials for enclosures of measurement instruments, particularly regarding the impact of minor compositional changes such as pigments and fillers, remains largely unexplored. Thus, the current study aims to fill this research gap by systematically investigating whether combinations of common insulating materials with various additives consistently meet the HB, HB40, and HB75 flammability criteria, potentially streamlining safety certification processes for measurement instrument enclosures. Motivation and Objective: The present study is situated in this context of balancing safety compliance with practical material selection. We focus on the horizontal 50 W flame test (EN 60695-11-10, method A) as a baseline flammability assessment for insulating enclosure materials. This was in order to systematically investigate how different polymer materials and their additive combinations influence the HB classification, and whether multiple formulations can be deemed equivalent in fire behaviour. Unlike most previous studies that concentrate on achieving the highest flame rating (V-0) using dedicated flame retardants, our work examines more subtle formulation changes (different base polymers, color pigments, and fillers) and their effect on the HB, HB40, or HB75 category achieved. We tested 64 material combinations, encompassing several common thermoplastic and thermoset polymers used in instrument casings, along with various pigment and filler additions. By analyzing such a broad matrix of compositions, we aim to identify patterns or groupings of materials that consistently exhibit the same flammability classification. The novelty of this research lies in its scale and its emphasis on \"equivalent performance\" among different compositions--an area not extensively covered in the literature. The ultimate objective was to provide guidance on material formulation for manufacturers: if certain additives or pigments are proven not to degrade (or even improve) the flame resistance of a base material, these could be interchanged with minimal safety risk, potentially obviating the need for separate certification tests for each variant. In summary, this study seeks to place fire safety compliance in a broader materials engineering context, exploring how the intelligent selection of polymer/additive combinations can maintain required flammability standards (HB, HB40, HB75) for measuring instrument enclosures without the repetitive testing of every minor variation. The findings contribute to both the scientific understanding of polymer flammability and the practical effort to optimize material design for safety, thereby supporting innovation in instrument enclosure design under the stringent requirements of regulations and standards. Although horizontal burning tests are commonly used to assess material flammability, the existing literature rarely addresses how minor changes in composition--such as the addition of pigments or inert fillers--affect HB classification. This study fills that gap by systematically investigating whether such compositional variations impact the horizontal burning behaviour of materials used in measurement instrument enclosures.