diff --git a/src/StringRepresentation.cpp b/src/StringRepresentation.cpp
index 89def44..f3bf6f2 100644
--- a/src/StringRepresentation.cpp
+++ b/src/StringRepresentation.cpp
@@ -24,19 +24,21 @@ using namespace std;
 
 namespace libforefire {
 
-// static variables initialization
-size_t StringRepresentation::currentLevel = 0;
-ostringstream StringRepresentation::outputstr("");
+// The output buffer, the nesting level and the GeoJSON aggregation state used
+// to be statics and file globals here, so two simulations printing at the same
+// time wrote into one buffer. They are members now.
+//
+// For GEOJSON mode we aggregate rings per top-level front. Each top-level
+// feature (currentLevel==1) is a vector of rings, where each ring is a vector
+// of coordinate strings.
+//
+// writedOnce is deliberately left shared for now. Unlike the rest, making it
+// per-instance is an observable change: output() skips a representation whose
+// domain has no front once anything has been written, so a second
+// representation in the same session would gain a first output file it does
+// not produce today. That is a behaviour question for the coupled runs, not a
+// mechanical one, and it belongs with the state work in #175.
 bool writedOnce = false;
-string outPattern;
-FireDomain* domain = 0;
-
-// --- GEOJSON Aggregation Variables ---
-// For GEOJSON mode we aggregate rings per top-level front.
-// Each top-level feature (currentLevel==1) will be represented as a vector of rings,
-// where each ring is a vector of coordinate strings.
-static bool firstGeoFeature = true;  // used when outputting the feature list
-static std::vector< std::vector<std::string> > geojson_current_feature;
 
 StringRepresentation::StringRepresentation(FireDomain* fdom) : Visitor() {
     lastLevel = -1;
diff --git a/src/StringRepresentation.h b/src/StringRepresentation.h
index 761f5c4..8fbad99 100644
--- a/src/StringRepresentation.h
+++ b/src/StringRepresentation.h
@@ -18,13 +18,22 @@ namespace libforefire {
 class StringRepresentation: public Visitor {
 
 	FireDomain* domain;
-	static size_t currentLevel;
+
+	/* These were statics, shared by every simulation in the process: two
+	 * concurrent print[] calls interleaved into one buffer. */
+	size_t currentLevel = 0;
+	bool firstGeoFeature = true; /*!< first feature of the GeoJSON list */
+	std::vector< std::vector<std::string> > geojson_current_feature;
 
 	double updateStep;
 
 public:
 
-	static ostringstream outputstr;
+	/*! \brief buffer the representation is built into
+	 *
+	 * Was static, so two simulations printing at once interleaved into one
+	 * buffer. Command::dumpString reads it, hence public. */
+	ostringstream outputstr;
 
 /*	StringRepresentation();*/
 	StringRepresentation(FireDomain*);